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UNIVERSITY  OF  ILLINOIS 

Agricultural  Experiment  Station 


BULLETIN  No.  133 


EAR  ROTS  OF  CORN 


BY  THOMAS  J.  BURRILL  AND  JAMES  T.  BARRETT 


URBANA,  ILLINOIS,  FEBRUARY,  1909 


SUMMARY  OF  BULLETIN  No.  133 

At  husking  time  or  before,  certain  ears  of  corn  (maize)  are  found  in  the 
field  covered  with  and  penetrated  by  a  whitish,  or  sometimes  a  pinkish,  mold. 
Affected  ears  become  very  light  in  weight  and  present  all  the  evidences  of  dry 
decay.  This  state  of  things  has  long  been  known  and  observed  thruout  the  corn 
growing  regions  of-  the  United  States  and  probably  elsewhere.  There  does  not 
seem  to  be  much  variation  in  the  occurrence  or  amount  of  infection  due  to  soil, 
date  of  planting,  variety  of  corn,  etc.,  except  that  there  is  more  of  it  in  fields 
continuously  devoted  to  this  crop.  Pages  65-69 

Though  not  usually  accounted  serious,  the  losses  are  far  greater  than  are 
commonly  supposed,  and  vary  in  different  years  and  in  different  fields  up  to 
ten  or  even  more  percent  of  the  entire  crop,  or  up  to  at  least  $5,000,000  for  one 
year  in  the  State  of  Illinois.  Pages  69-70 

The  active  agents  of  the  destruction  are  several  species  of  parasitic  fungi, 
among  which  one  does  by  far  the  most  damage — probably  90  percent  of  the 
whole  amount.  This  is  botanically  known  as  Diplodia  Zeae  (Schw.)  Lev.  It 
lives  over  winter  on  old  infected  ears  and  stalks,  from  which  there  are  sent  out 
the  following  season  myriads  of  spores  which  are  widely  distributed  by  the 
wind.  Under  favoring  conditions  (mainly  the  presence  of  moisture  at  the  right 
date)  these  spores  start  new  infections  in  the  green  ears..  Of  this  fungus  see: 
Life  history  on  the  ears,  page  73;  Life  history  on  stalks,  page  74;  Growth 
in  cultures,  page  76;  Effects  of  acids  and  alkalis,  page  78;  Germination  of 
spores,  page  80 ;  Distribution  of  spores,  page  81 ;  Inoculation  experiments,  page 
83;  Synonomy,  page  94.  Pages  70-85 

At  least  three  other  species  of  fungi,  all  belonging  to  the  genus  Fusarium, 
attack,  with  somewhat  similar  results,  the  developing  ears  of  corn  in  the  field. 
Their  full  life  histories  in  the  field  have  not  been  worked  out,  but  infection 
originates  from  wind-borne  spores.  No  ears  become  diseased  except  from 
spores  reaching  them  from  an  outside  source ;  that  is,  the  ears  are  never  affected 
by  means  of  anything  working  up  through  the  stalk.  Pages  85-91 

Ears  in  the  field  are  sometimes  injured  by  one  or  more  species  of  bacteria 
but  this  kind  of  loss  from  these  minute  organisms  seems  to  be  comparatively 
slight.  Pages  91-92 

So  far  at  least  as  the  Diplodia  fungus  is  concerned,  the  disease  is  certainly 
subject  to  control.  Since  the  spores  come  from  old  infected  ears  and  stalks 
their  destruction  must  reduce  at  least  the  loss  for  the  new  crop,  and  a  system 
of  rotation  which  excludes  corn  for  two  years  from  or  near  the  given  plat  of 
ground  will  assuredly  help  to  prevent  infection.  Pages  92-94 


64 


EAR  ROTS  OF  CORN 

BY  THOMAS  J.   BURRILL,   CHIEF  IN   BOTANY,  AND 
JAMES  T.  BARRETT,  FIRST  ASSISTANT  IN  BOTANY 

GENERAL  OBSERVATIONS 

APPEARANCE  Every  one  who  has  had  anything  to  do  with  harvesting 
corn  has  noticed  at  least  an  occasional  ear  that  differed 
remarkably  from  the  normal  ones  in  being  more  or  less  covered  with 
and  penetrated  by  mold.  In  many  cases  the  husks  and  silk  are  also 
involved  and  appear  cemented  together  and  to  the  ear  by  a  mass  of 
white,  cobwebby  filaments.  (PI.  I.) .  At  the  same  time  the  parts  affected 
have  lost  their  substance,  are  light  in  weight  and  brittle  in  texture. 
Sometimes  such  diseased  ears  are  seldom  found  at  the  time  of  husking, 
often  they  are  not  uncommon. 

Upon  closer  study  it  soon  becomes  apparent  that  there  are  several 
kinds  of  these  ear  rots,  or  at  least  that  there  are  differences  which  seem 
fairly  constant  when  numerous  specimens  are  carefully  examined.  It 
is  thus  possible  to  divide  the  affected  ears  into  several  groups,  four  of 
which  are  described  in  this  paper.  They  are  discussed  Under  the  names 
of  the  parasitic  fungi  to  which  the  effects  are  attributed,  as  follows: 
(1),  Diplodia;  (2),  Fusarium  I. ;  (3),  Fusarium  II. ;  (4),  Fusarium 
III.  These  names  are  defined  further  along  and  each  form  of  rot  is 
described  later  under  its  own  heading. 

Some  of  these  ear  rots  are  so  similar  that  the  casual  observer 
rarely  entertains  any  suspicion  of  there  being  but  one  form.  The 
resemblances  are  so  complete  in  some  instances  that  the  removal  of  the 
husk  and  sometimes  a  microscopical  examination  are  needed  for  the 
classification  of  the  variety.  Commonly,  however,  in  fairly  advanced 
stages  of  the  disease  one  or  more  characteristic  differences  are  apparent. 
The  two  forms  most  likely  to  be  confused,  and  the  only  ones  which  as 
a  rule  involve  the  husks,  may  be  distinguished  by  the  color  of  the  mold- 
like  growth.  In  the  case  of  the  Diplodia  disease  this  is  white,  while  in 
that  of  Fusarium  II.  it  is  pink  to  red. 

The  first  indication  that  ears  of  corn  are  diseased  is  a  fading  of 
the  bright  green  of  the  husks  to  a  pale  yellowish  green  color.  In  the 
Diplodia  disease  this  change  goes  on  gradually,  and  under  favorable 
conditions  quite  rapidly,  until  the  entire  ear  has  an  appearance  of  pre- 
mature ripening.  While  this  change  of  color  on  the  outside  is  pro- 
gressing one  finds  that  the  inner  husks  have  not  only  lost  their  normal 
color,  but  are  more  or  less  tinged  with  brown,  particularly  along  the 
advancing  margin  of  the  diseased  area.  (PI.  I.).  This  condition  is 
much  more  striking  in  some  ears  than  others.  With  the  advance  of  the 
disease  the  outer  husks  grow  darker  and  darker,  frequently  becoming 
dirty  to  sooty  black  in  appearance,  when  they  present  a  striking  con- 
trast to  those  of  normally  ripened  ears. 

This  description  also  applies  to  the  disease  produced  by  Fusarium 
II.,  although  no  entirely  decayed  ear  due  to  this  organism  has  been 

65 


66  BULLETIN  No.  133  [February, 

found.  In  this  case  infection  always  begins  at  the  tip  and  proceeds 
downward,  rarely  involving  more  than  half  the  ear.  In  both  forms 
badly  diseased  ears  are  tightly  clasped  by  the  dry,  brittle  husks  except 
in  cases  where  infection  by  Diplodia  takes  place  in  the  base  of  the  ears 
too  late  in  the  season  for  the  entire  ear  to  become  diseased.  Many  of 
the  badly  diseased  ears  on  account  of  their  lightness  in  weight  remain 
upright. 

The  diseased  ears  shrivel  up  more  or  less,  become  darker  in 
color  and  lighter  in  weight.  The  kernels  are  also  shriveled,  are  very 
brittle,  and  are  loosely  attached  to  the  more  or  less  rotten  cob.  The 
silk  is  moldy  and  adheres  by  the  mass  of  fungous  threads  to  the  inner 
husks  and  corn.  Under  the  microscope  the  starch  is  seen  to  be  variously 
corroded  and  notched,  and  it  is  frequently  discolored.  The  germ  por- 
tion of  the  kernels  is  most  frequently  killed,  or  if  not  is  always  injured. 
Microscopical  examination  shows  that  the  fungus  penetrates  all  parts 
of  the  ear,  sometimes  extending  into  and  badly  injuring  the  shank. 
No  ill  effects  on  other  parts  of  the  corn  plant  have  been  observed. 

The  other  Fusarium  diseases  mentioned  produce  very  different 
effects  on  the  ears  and  are  commonly  not  detected  in  the  field  until  the 
husks  are  removed.  Fusarium  I.  attacks  only  those  husks  which  come 
into  contact  with  the  diseased  surface  of  the  ear.  The  cob  is  not  so 
generally  diseased  as  in  the  above  described  forms.  A  third  Fusarium 
species,  Fusarium  III.,  attacks  the  ends  of  scattered  individual  grains, 
causing  them  to  crack  open  and  the  starchy  contents  to  become  crumbly. 
Mycelium  and  spores  are  found  in  this  crumbly  starch  which  is  con- 
siderably corroded.  (PI.  III.,  Fig.  I.). 

SEASONAL  The  premature  yellowing  of  the  husks  on  plants  other- 

OCCUREENCE  wise  healthy  is,  as  previously  stated,  an  indication  that 
a  diseased  condition  exists  which  is  usually  attributa- 
ble to  infection  by  some  one  of  the  field  rot  organisms.  This  condition 
in  the  case  of  the  Diplodia  disease  may  be  found  in  fields  soon  after 
the  fertilization  of  the  corn  has  taken  place,  the  number  of  infected 
ears  increasing  more  or  less  thruout  the  season.  Very  little  is  known 
as  to  the  time  of  maximum  infection  by  the  various  species  of  Fu- 
sarium which  cause  these  diseases.  Two  of  the  forms,  as  previously 
stated,  can  rarely  be  detected  until  the  corn  is  husked  and  the  third  has 
not  been  well  studied  in  the  field. 

Infection  is  certainly  in  the  case  of  Diplodia  and  very  probably  in 
that  of  the  other  fungi  brought  about  by  means  of  spores.  It  is  known 
that  under  favorable  conditions  Diplodia  spores  are  produced  in  large 
numbers  during  the  summer  and  fall  in  infected  fields,  and  that  these 
spores  are  carried  considerable  distances  by  the  wind.  They  are  scat- 
tered thruout  the  fields  where  they  find  favorable  germinating  condi- 
tions, and  yet  the  fungus  has  not  been  found  on  any  other  plant,  nor 
has  any  other  part  of  growing  corn  other  than  the  ear  and  its  shank 
been  found  to  be  infected. 

The  best  spore-producing  periods  seem  to  follow  hot,  rainy  weather 
preceded  by  more  or  less  continued  dry  spells,  the  reason  for  which 
will  be  stated  later. 


1909]  EAR  ROTS  OF  CORN  67 

Since,  then,  under  favorable  conditions  the  spores  are  produced 
in  such  large  numbers  thruout  the  season,  the  matter  of  little  or  much 
infection  depends  in  part,  at  least,  on  these  spore-producing  periods 
coming  at  a  time  when  the  corn  is  in  the  most  susceptible  condition  for 
infection.  Of  a  large  number  of  inoculations  made  during  the  season 
of  1907  the  highest  percentage  of  infections  was  obtained  from  those 
made  on  August  31,  from  a  pure  culture,  when  the  corn  was  in  the 
thick-milk  stage.  It  is  at  this  period  and  later,  in  the  development  of 
the  corn,  that  the  larger  percent  of  infected  ears  in  the  field  begins  to 
show. 

These  diseases  occur  with  more  or  less  severity  in 
almost  every  locality  in  Illinois  where  corn  is  grown, 

Ox    HJUA.Ll.Lx,  .     '..  .  -  ~     . 

SOIL,  ETC.  and  the  same  or  similar  ones  have  been  reported  trom 

Nebraska,  Arkansas,  Iowa,  Indiana,  Ohio,  and  North 
Carolina.  It  \is  quite  probable  that  no  corn-growing  section  is  without 
at  least  some  of  the  diseases.  Corn  grown  on  the  rich,  black  land  of 
our  corn  belt  is  more  subject,  on  the  whole,  to  them  than  that  on  higher 
and  thinner  soils,  although  a  few  seemingly  contrary  reports  have  been 
received. 

A  part  of  the  report  from  Vermilion  County  is  as  follows : 
"The  field  had  about  5  acres  of  what  we  call  low,  black  land ;  this  always 
has  the  best  corn  and  this  year  we  seemed  to  find  the  most  rotten  corn  in  this 
part  of  the  field.  There  seems  to  be  less  rotten  [corn]  on  high  ground  where 
plenty  of  manure  had  been  used.  I  also  noticed  in  another  field  containing 
some  of  the  same  black  soil  that  the  rotten  [corn]  is  thicker  than  in  any  other 
part  of  the  field.  We  do  not  find  it  this  year  in  quite  the  same  form  as  last 
year.  You  can  tell  by  the  looks  of  the  husks  if  an  ear  is  rotten.  Last  year 
many  rotten  ears  had  just  as  bright  husks  as  the  good  ears  and  you  could  not 
tell  until  you  had  husked  an  ear  whether  it  was  good  or  bad.  This  year  the 
husks  on  the  rotten  ears  are  black  or  nearly  so." 

The  following  is  from  a  report  from  Douglas  County: 

"I  farmed  a  33-acre  field  belonging  to  a  man  who  does  not  sow  clover  at  all 
(this  piece  being  in  corn  about  13  years).  And  the  amount  of  rot  was  large, 
especially  on  the  low  ground.  I  do  not  know  what  amount  of  rot  was  on  the 
field  last  year.  I  notice  that  as  a  rule  the  rotten  corn  appears  to  be  in  spots, 
say  two  or  more  ears  near  by,  especially  in  proximity  to  tiles  or  drains, — our 
tiles  and  ditches  are  not  working  well  in  this  section  at  present  and  the  low 
ground  is  wet  much  of  the  season  when  we  have  a  good  deal  of  rain.  Of 
course  there  is  some  rotten  corn  on  the  high  ground." 

A  report  from  Wayne  County  states : 

"Found  a  larger  percent  about  the  old  stockyards  and  heavily  manured 
spots." 

The  greater  the  number  of  old  stalks  and  the  greater  the  supply 
of  moisture,  the  better  the  opportunity  for  a  continual  and  rapid  propa- 
gation of  the  most  destructive  of  these  fungi,  thus  subjecting  the  corn 
grown  at  such  a  place  to  a  much  greater  chance  of  inoculation. 

EARLY  AND  There  seems  to  be  some  difference  of  opinion  as  to 

LATE  PLANTED      the  extent  of  rot  on  early  and  late  planted  corn.    This 
CORN  difference  has  been,  the  past  two  seasons,  in  favor  of 

the  early  planted,  the  majority  of  the  reports  stating 
that  it  showed  more  rot.  Fifty-five  percent  said  that  there  was  more 


68  BULLETIN  No.  133  [February, 

rot  in  the  early  planted,  33  percent  in  the  late  and  12  percent  found  no 
perceptible  difference.  In  1906  a  very  dry  summer  was  broken  by 
heavy  rains  while  the  early  corn  was  beginning  to  silk.  Everything 
was  favorable  for  the  production  of  Diplodia  spores,  and  as  a  result 
much  corn  rotted.  Sixty-one  percent  of  all  reports  for  that  season 
stated  that  the  early  corn  was  more  badly  rotted.  Such  differences 
cannot  be  attributed  to  differences  in  susceptibility  of  early  and  late 
corn,  only  in  so  far  as  influenced  by  weather  conditions.  Warm,  moist 
weather  favors  the  development  of  the  diseases  and  the  production  of 
spores,  and  when  these  conditions  obtain  at  the  most  susceptible  period 
in  the  development  of  the  ears  everything  is  favorable  for  infection. 
Inoculations  made  late  in  the  season  on  corn  in  the  right  condition 
grew  much  more  slowly  than  earlier  ones,  due,  no  doubt,  to  CQO! 
weather. 

,T,  vn,m     From  careful  data  collected  by  the  department  and 

UJN    UJjU   UK  .Nx. W         ,  .        ,  .       . 

CORN  GROUND        from  reports  sent  in  by  corn  growers,  it  is  very  ap- 
parent that,  as  a  rule,  ear  rot  is  more  prevalent  and 
destructive  in  fields  planted  successively  to  corn  than  in  those  on  which 
a  good  system  of  rotation  is  practiced.    There  are,  of  course,  excep- 
tions to  this,  but  they  are  rare.    The  old  stalks  and  diseased  ears  when 
left  in  the  field  are  known  to  carry  the  Diplodia  fungus  over  winter, 
and  to  offer  opportunity  for  infection  the  following  season. 
A  report  from  Fulton  County  says: 

"There  was  about  three  times  as  much  rot  on  the  fourth  crop  of  corn  on 
the  same  ground  as  on  the  first." 

During  the  fall  of  1907  some  field  counts  were  made  at  husking 
time  as  to  the  relative  amounts  of  the  different  forms  of  rot  in  fields 
both  old  and  new  to  corn*  on  the  same  farm.  The  old  ground  produced 
the  most  rot  in  every  case. 

Of  the  reports  sent  in  the  past  two  seasons  65  percent  stated  that 
more  field  <rot  is  found  on  old  corn  ground,  16  on  the  new,  and  19  said 
there  was  no  difference. 

Instances  are  not  uncommon  where  one  or  more  sides  of  a  field 
for  a  number  of  rows  are  much  more  affected  than  the  interior,  indi- 
cating a  source  of  infection  without  the  field.  In  view  of  the  easy 
transmission  of  the  spores  by  the  wind,  this  is  entirely  possible,  and 
also  accounts  for  the  fact  that  corn  on  new  ground  may  become  badly 
diseased. 

A  report  from  De  Witt  County  says : 

"The  outside  of  my  fields  had  more  rotten  corn  than  the  inside,  and  the  east 
sides  more  rotten  than  the  other  sides." 

In  May,  1908,  a  clover  field  was  visited  which  produced  a  crop  of 
corn  in  1906  badly  damaged  with  rot.  The  field  was  sown  to  oats  and 
clover  in  1907,  and  in  1908  most  of  the  field  planted  to  corn.  Old  corn 
stalks  were  plentiful  in  the  clover  field  and  most  of  those  examined 
were  abundantly  infected  with  the  Diplodia  fungus.  The  stalks  were 
not  all  covered  by  earth  in  the  portion  of  the  field  planted  to  corn  and 

*  "New  to  corn,"  meaning  not  previously  in  corn  for  at  least  two  years. 


1909]  EAR  ROTS  OF  CORN  69 

these,  too,  carried  numerous  spores.  The  latter  were  found  to  be 
capable  of  germination. 

Even  though  all  stalks  in  the  corn  field  had  been  covered,  there 
remained  abundant  opportunity  of  infection  from  the  clover  field.  This 
is  but  one  instance  of  a  condition  which  is  not  at  all  uncommon.  The 
first  requisite  of  an  epidemic  of  disease  is  the  presence  of  a  sufficient 
number  of  spores  or  germs  capable  of  producing  it,  and  their  ^absence 
'is  a  sure  prevention. 

A  correspondent  from  Springdale,  Arkansas,  writing  under  date 
of  October  10,  1908,  remarks: 

"Will  say  that  out  of  500  ears  gathered  in  a  field  planted  the  third  straight 
year  in  corn,  4%  were  affected  by  this  trouble." 

No  definite  data  have  been  collected  as  to  the  sus- 

.  . 

ceptibihty  of  the  various  varieties  of  corn  to  the  rot 
diseases.  Of  those  mentioning  the  matter  in  reports  forwarded  to  us 
relative  to  the  1906  crop,  50  percent  said  yellow  and  the  other  50  per- 
cent that  white  was  the  most  susceptible.  The  reports  of  1907  showed 
that  some  form  of  rot  occurred  with  six  different  varieties,  but  few 
statements  as  to  comparative  amounts  were  made.  One  who  breeds 
and  raises  corn  for  seed  reported  that  the  rot  was  much  worse  on 
certain  rows  growing  directly  beside  others  where  each  row  came  from 
a  separate  seed  ear. 

AMOUNT  OF   INJURY 

Upon  careful  observation  and  inquiry  it  has  been  ascertained  that 
the  loss  is  much  greater  than  is  ordinarily  supposed  and  sometimes 
amounts  to  surprising  percentages.  In  the  autumn  of  1906  fields  were 
examined  by  the  writers  in  which  as  high  as  10  percent  of  the  ears 
were  so  attacked,  and  reports  of  actual  counts  were  received  in  which 
as  much  as  20  percent  of  rotten  ears  were  recorded.  Reports  of  from 
10  percent  to  15  percent  were  not  very  unusual. 

Upon  the  best  estimates  that  could  be  made  with  the  aid  of  hun- 
dreds of  correspondents  in  all  parts  of  the  state,  the  conclusion  has 
been  reached  that  in  1906  the  destruction  from  the  cause  in  question 
amounted  to  4.5  percent  of  the  entire  crop,  and  in  1907  to  about  2  per- 
cent of  the  produce  of  the  state  for  that  year.  When  the  enormous 
total  of  the  corn  crop  of  Illinois  is  considered,  the  losses  reach  magni- 
tudes which  necessarily  arrest  attention  and  imperatively  call  for  in- 
vestigation. 

The  State  Department  of  Agriculture  reports  the  corn  crops  of 
Illinois  in  recent  years  as  follows: 

1903  264,087,431  bushels,  worth  $  95,071,475. 

1904  344,133,680   "     "  134,212,135. 

1905  382,752,063   "     "  145,445,784. 

1906  347,169,585   "     "  124,981,051. 

Of  the  crop  for  1906  there  were,  therefore,  lost  about  15,622,631 
bushels,  worth  $5,620,147.  There  was  much  less  of  the  rot  in  1907, 
but  the  loss  figured  in  a  similar  way  from  the  best  data  at  hand  was 
not  less  than  $2,000,000.  These  figures  at  least  indicate  enormous 


70  BULLETIN  No.  133  [February, 

financial  damage  year  by  year  which  has  not  heretofore  been  duly 
appreciated  on  the  part  of  the  farmers  or  of  others  interested.  While 
the  rots  have  long  been  casually  known  and  the  variations  in  propor- 
tions of  affected  ears  have  often  been  remarked,  there  is  good  reason  to 
suppose  that  there  has  been  really  considerable  increase  during  later 
years.  From  the  information  now  gained,  further  increase  is  very 
probable  upon  land  persistently  devoted  to  this  crop.  The  amount  for 
1906  was  undoubtedly  far  beyond  an  average ;  but  this  may  easily  be 
much  surpassed  some  year  not  now  distant,  while  the  general  average 
loss,  unless  wisely  prevented,  is  pretty  sure  to  increase  more  or  less 
constantly. 

If  all  this  is  true  for  Illinois,  the  figures  for  the  whole  country 
must  reach  enormous  proportions.  While  it  is  probable  that  there  is 
more  absolute  loss  in  Illinois  than  in  any  other  state,  this  seems  but 
due  to  the  fact  that  there  is  more  corn  produced  and  that  the  best  land 
is  more  often  continuously  planted  to  corn  year  after  year.  Certain 
it  is  that  similar  losses  are  common  thruout  the  area  extending  from 
Michigan  to  Arkansas  and  from  Nebraska  to  North  Carolina,  as  our 
own  observations  and  correspondence  prove.  While  so  often  consid- 
ered negligible  locally,  the  total  loss  in  the  United  States  must  some- 
times amount  to  at  least  $25,000,000  in  one  year. 

CAUSES   OF  EAR  ROTS 

Most  people  still  suppose  that  molds  are  the  direct  results  of  the 
prevailing  conditions.*  Dampness  and  confined  space  are  most  fre- 
quently thought  of  as  the  causes  of  moldiness.  When  a  piece  of  bread 
is  shut  up  in  a  tin  box  or  when  placed  in  a  damp  cellar,  it  soon  be- 
comes covered  with  a  cobwebby  growth  soon  taking  on  a  characteristic 
color,  as  bluish  or  blackish,  and  having  a  musty  odor.  These  molds 
are  plants;1  there  are  many  kinds  of  them.  They  reproduce  themselves 
and  grow  when  once  started  after  the  fashion  of  the  higher,  better 
known  plants.  Instead  of  seeds  they  produce  spores  which  differ  from 
seeds  in  being  much  more  simple  in  structure  and  in  being  too  small 
to  be  seen  singly  by  the  unaided  eye.  Sometimes,  however,  they  are 
easily  so  seen  in  masses  as  a  cloud  of  dust  arising  from  a  disturbed 
surface.  In  fact  it  is  mainly  the  spores  which  give  to  any  given  mold- 
crop  its  characteristic  color.  They  are  produced  in  enormous  numbers, 
absolutely  innumerable  even  from  a  small  area  of  an  infected  sub- 
stance; and  it  is  to  this  abundance  of  "fruit"  and  the  microscopic  size 
of  the  individual  spores,  permitting  easy  and  wide  carriage  by  the  air, 
that  the  plants  everywhere  spring  into  existence  when  conditions  favor 
germination  and  growth.  Unlike  the  higher,  green-leaved  plants,  they 
do  not  require  light  for  development.  They  grow  only  on  organic 
matter,  on  food  already  prepared — in  this  respect  like  animals.  But 


•A  correspondent  says:  "I  have  never  considered  the  loss  of  corn  by  the  rotten  _  ears 
found  at  husking  time  due  to  any  other  cause  than  water  entering  the  husk  and  remaining 
during  a  warm  day  or  two  which  seemed  to  steam  the  ear  and  cause  it  to  shrivel  and  then 
decay  more  or  less,  as  the  case  nrght  be."  Another  says:  "Mold  depends  on  weather  con- 
dit:ons  more  than  anything  else."  Another,  "The  prevailing  opinion  among  farmers  is  that 
dry  weather  is  the  cause  of  dry  rot." 


1909]  EAR  ROTS  OF  CORN  71 

they  are  really  plants,  each  producing  "seed"  after  its  kind  from  which, 
and  only  from  which,  it  continues  its  existence.  Their  generations  are 
shorter  but  they  have  the  same  round  of  germination,  growth,  fruit- 
age and  death  as  do  other  living  beings.  Origination,  except  in  this 
method,  does  not  occur.  No  matter  how  moist  the  air  or  how  devoid 
of  ventilation  the  space  or  how  favorable  the  temperature,  a  piece  of 
bread  never  can  become  moldy,  indeed  can  never  decay  at  all,  without 
a  seeding  with  spores  or  their  substitutes.  And  no  special  kind  of  mold, 
or  other  fungous  growth  can  develop,  without,  to  start  with,  the  spores 
of  this  particular  kind  or  species. 

Molds  belong  to  the  great  group  of  plants  called  fungi — a  group 
including  besides  molds  and  mildews,  all  such  diverse  kinds  of  plants 
as  the  shelf-fungi  on  deadwood,  puff-balls,  mushrooms,  toadstools,  and 
a  host  of  microscopic  forms  among  which  are  the  rusts  and  smuts 
upon  cereals.  The  greater  number  of  the  thousand  and  more  kinds 
of  fungi  grow  only  on  dead  organic  matter.  Their  function  is  to  induce 
decay,  decomposition,  putrefaction,  etc.  These  are  called  saprophytes. 
But  some  are  capable  of  attacking  the  living  bodies  of  plants  or  ani- 
mals. These  are  called  parasites.  Again,  some  of  the  latter  may  live, 
either  as  saprophytes  or  parasites,  while  others  are  strictly  limited  to 
living  bodies  and  often  to  a  particular  species,  called  the  host,  for  each 
parasite.  Thus  the  large,  sooty  masses  seen  on  corn  stalks  or  ears  is 
made  up  of  the  spores  of  a  special  parasite  which  attacks  nothing  else 
than  the  maize  plant,  and  develops  only  on  this  plant  during  its  life- 
time. The  vegetative  portion  of  the  fungus — answering  in  some  sense 
to  the  roots,  stems,  and  branches  of  the  higher  plants — is  called  the 
mycelium.  In  molds  this  constitutes  a  cobwebby,  puffy  substance 
which  is  more  often  white.  The  spores  (fruit  bodies)  are  borne  on 
the  mycelium  or  upon  specially  modified  structures  arising  from  it. 
The  latter  are  of  wonderfully  varied  form  and  structure,  while  the 
mycelium  itself  is  characteristically  made  up  of  fine  filaments  or 
threads  with  comparatively  little  difference  in  form  for  different  spe- 
cies. Under  the  microscope  the  spores  of  each  kind  are  usually  recog- 
nizable and  often  are  very  distinct. 

Now  the  ear  rots  of  maize  are  due  to  definite  species  of  mold-like 
parasites.  So  far  as  is  known,  these  grow  on  nothing  but  the  corn 
plant,  though  some  of  them  may  have  wider  possibilities.  The  greatest 
amount  of  destruction  is  made  by  one  kind  called  Diplodia  Zeae.  There 
are  numerous  species  of  Diplodia  known  on  various  hosts  or  sub- 
stances, but  this  one  seems  to  grow  only  upon  maize.  It  was  first  found 
producing  its  characteristic  spores  on  dead  stalks  and  was  then  con- 
sidered a  purely  saprophytic  plant.  When  in  recent  years  the  mold  on 
many  living  ears  was  traced  to  Diplodia  the  suspicion  was  strong  that 
it  was  a  distinct  species,  but  our  investigations  have  clearly  shown  that 
the  growth  on  the  green  ear  and  that  upon  the  dead  stalks  is  one  and 
the  same  thing.  This  fungus  is,  therefore,  a  parasite  during  a  part  of 
its  life  and  a  saprophyte  at  other  times. 

It  is  evident  now  how  the  fungus  lives  over  from  year  to  year, 
and  how  the  growing  ears  gain  infection.  As  will  be  fully  shown 


72  BULLETIN  No.  133  [February, 

later,  the  spores  are  produced  in  abundance  during  the  summer  upon 
old  stalks,  even  from  those  lying  on  the  ground  the  second  year,  and 
these  spores  are  readily  carried  by  the  wind  as  dust.  Lodging  upon 
the  developing  ear  they  germinate  when  the  conditions  are  favorable. 
For  this  moisture  is  a  necessity ;  temperature  has  something  to  do  with 
it.  Given  the  same  distribution  of  viable  spores  there  will  still  be  much 
seasonal  difference  in  the  amount  of  rot,  due  to  the  differences  in  influ- 
encing conditions,  without  at  all  supposing  that  the  conditions  originate 
the  trouble.  The  rot  could  not,  does  not,  occur  without  the  infecting 
spores,  no  matter  what  the  weather  may  be,  what  the  soil  may  be,  or 
what  state  soever  the  corn  plant  may  be  in.  Conditions  simply  favor 
or  do  not  favor  the  spore  growth.  With  spores  capable  of  germination 
on  the  green  ears,  rot  is  likely  to  follow  moist  weather  because  this 
permits  the  growth  of  the  fungus.  Then  the  state  of  the  corn  plant 
has  something  to  do  with  it.  Undoubtedly  a  difference  exists  at  differ- 
ent times  concerning  its  power  of  resistance.  It  is  more  susceptible 
to  infection  at  one  period  than  at  another,  other  things  being  equal. 
The  maximum  of  rot  will  occur  when  numerous  spores  of  the  fungus 
are  deposited  on  the  ears  at  a  time  when  these  are  easiest  infected  and 
when  the  weather  conditions  most  favor  the  fungus  in  its  growth. 
Much  difference  may  therefore  be  anticipated  in  the  amount  of  rot 
from  year  to  year,  due  to  the  coincidence  or  otherwise  of  the  favoring 
conditions. 

The  principal  other  fungi  which  have  been  found  as  agents  of  ear 
rots  of  corn  are  species  of  the  genus  Fusarium.  Three  of  these  have 
been  distinguished,  to  be  described  later.  To  the  casual  observer  their 
effects  on  corn  are  identical  with  the  result  produced  by  Diplodia,  but 
on  closer  comparison  differences  are  discoverable.  All  show  mold-like 
growth.  All  cause  decay  of  the  part  of  the  ear  infected — silk,  kernels, 
cob,  husks  and  sometimes  shank — causing  these  parts  at  length  to  be- 
come dry,  brittle,  and  light  in  weight. 

In  addition  to  these  fungi  certain  bacteria  sometimes  cause  a  rot 
of  the  developing  ears,  producing  final  results  somewhat  similar  to 
those  described.  This  form  does  not  seem  to  be  very  common  and  has 
not  been  much  studied.  Possibly  more  than  one  species  thus  infest 
corn  ears.  Further  investigation  must  be  made  before  much  may  be 
•  known  concerning  the  part  played  by  bacteria  in  these  field  rots  of 
maize. 

In  a  word,  then,  the  rots  observed  upon  the  ears  of  corn  in  the 
field  are  due  to  certain  parasitic  plants,  mold-like  in  appearance,  be- 
longing to  the  genera  Diplodia  and  Fusarium,  and  to  one  or  more  spe- 
cies of  bacteria.  The  amount  of  destruction  at  any  particular  time 
depends  upon  the  varying  prevalence  of  the  spores  of  these  parasites 
in  association  with  conditions  existing  at  the  given  period.  It  is  worthy 
of  remark  that  in  no  case  has  natural  infection  by  these  parasites  been 
discovered  upon  any  other  part  of  the  immature  corn  plant  save  the 
ears  and  their  belongings.  Upon  the  latter  infection  always  begins 
externally  from  air-distributed  spores. 


1909]  EAR  ROTS  OF  CORN  73 

DIPLODIA  ZEAE    (SCHW.)    LEV. 


LIFE  HISTORY  mycelium  of  the  Diplodia  organism,  as  it  occurs 

ON  EARS  m  the  active  growing  condition  on  the  ear  and  inner 

husks,  is  white  in  color  and  the  much  branched  threads 
are  about  4/u,*  in  diameter.  With  age  and  more  or  less  drying  up  of  the 
diseased  tissue  the  size  of  the  newly  formed  threads  become  smaller, 
averaging  about  2.  5fi.  With  the  exception  of  a  slight  darkening  in 
color  of  portions  more  exposed  to  the  air  and  the  deep  coloring  of  that 
which  surrounds  and  goes  to  form  pycnidia  (fruit  vessels),  the  .color  of 
the  mycelium  remains  white. 

The  slender  threads  penetrate  the  young  tissue  of  the  grains,  cob, 
and  husks,  progressing  from  cell  to  cell  and  extracting  from  their  con- 
tents whatever  is  of  value  for  food.  After  the  ear  has  become  entirely 
involved  or  the  growth  of  the  parasite  somewhat  checked  by  the  ma- 
turing of  the  corn,  the  fungus  begins  to  form  its  reproductive  stage. 
This  consists  of  small  black  bodies  which  develop  in  the  husks,  cobs, 
and  more  rarely  in  the  grains,  and  which  contain  large  numbers  of 
purplish  brown,  rather  slender,  two-celled  spores,  25x5.2/x  in  size. 
(PI.  VIII.,  Fig.  1.).  If  4he  outer  husks  of  an  ear  in  a  well  advanced 
stage  of  the  disease  are  pulled  down,  the  spore  cases,  or  pycnidia,  will 
be  seen  as  minute  black  specks  slightly  elevated  above  the  surface. 
(PI.  IV.,  Fig.  2.).  An  examination  with  a  hand  lens  will  reveal  emerg- 
ing from  the  ruptured  tissue  a  short  neck  which  contains  a  centrally 
located  circular  pore  through  which  the  spores  escape.  The  pycnidia 
usually  occur  singly  on  the  husks,  but  several  grouped  together  in  a 
mass  is  not  an  infrequent  thing  where  conditions  have  been  favorable 
for  a  luxuriant  development  of  the  fungus,  as  under  bell  jar  conditions. 

The  pycnidia  which  develop  in  the  cob  are  much  more  irregular 
in  shape.  They  develop  principally  on  the  scales  which  surround  the 
inner  ends  of  the  corn  kernels,  hence  are  usually  not  detected  until  the 
ear  is  broken,  when  they  are  seen  forming  a  concentric  ring  of  black 
specks  about  the  margin  of  the  cob.  (PI.  VII.  ,  Fig.  1.).  They  are 
usually  not  at  all  or  only  slightly  imbedded  in  the  tissue  of  the  cob,  but 
are  seated  in  a  rather  dense  mass  of  white  mycelium  from  which  they 
originate.  A  longitudinal  section  of  an  ear  also  reveals  them  very  dis- 
tinctly. (PI.  III.,  Fig.  2.). 

Diseased  ears  left  in  the  field  under  natural  conditions  eventually 
develop  numerous  pycnidia  in  the  grains,  giving  them  a  black  appear- 
ance. In  May,  1907,  rotten  corn  of  the  1906  crop  was  scattered  over 
a  small  plot  of  ground  in  an  infection  experiment.  The  following 
March  some  of  this  corn  was  collected  and  was  found  as  described 
above.  Many  of  the  pycnidia  contained  spores,  some  of  which  were 
germinated  in  the  laboratory;  'but  most  of  them  were  old  and  empty 
and  at  that  time  all  development  of  the  organism  had  apparently  ceased. 

The  pycnidia  formed  in  the  cob,  as  previously  stated,  are  quite 
irregular  in  shape  ;  but  those  found  in  the  badly  diseased  grains  are 
somewhat  flask-shaped  with  the  comparatively  short  neck  projecting 

*  A  M  is   .001  of  a  millimeter  or   .0004  inch. 


74  BULLETIN  No.  133  [February, 

thru  the  testa.  (PI.  X.,  Fig.  2.).  It  will  be  noticed  from  the  figure 
that  the  wall  of  the  pycnidium  is  formed  by  the  interweaving  and  fusing 
of  the  hyphae,  or  mycelial  threads,  which  form  a  tangled  mass  between 
the  seed  coats  and  starchy  portion  of  the  grain.  The  wall  of  the  tubular 
neck  is  much  thicker  than  that  of  the  body  of  the  pycnidium  and  is 
mostly  made  up  of  thick-walled  cells,  with  others  having  thinner  walls 
lying  toward  the  outside.  Arising  from  the  inner  surface  of  the 
pycnidial  wall  are  numerous  simple  conidiophores,  or  spore  stalks,  on 
which  are  borne  the  two-celled,  brown  spores.  Among  these  are 
numerous  paraphyses,  or  stalk-like  forms  without  spores.  (PI.  X., 
Figs.  1  and  2.). 

The  development  of  the  Diplodia  fungus  is  not  confined  alone  to 
warm  summer  weather,  as  is  evidenced  by  an  examination  of  diseased 
ears  in  the  field  during  the  winter  and  early  spring.  January  29,  1908, 
a  stalk  of  sweet  corn  with  an  ear  attached  enclosed  in  the  husk  which 
had  been  inoculated  with  Diplodia  spores  on  August  10,  1907,  was 
brought  into  the  laboratory  from  the  field  where  it  had  been  all  winter, 
and  at  the  time  was  partially  covered  with  snow  and  ice.  On  remov- 
ing the  husks  a  mass  of  white  mycelium  in  an  active  condition  was 
revealed.  Pycnidia  were  present  in  various  stages  of  development  and 
the  spores  germinated  readily.  On  March  6,  1908,  some  diseased  ears 
of  field  corn  in  husks  on  stalks  left  in  the  field  in  the  fall  of  1907,  were 
examined  and  were  found  to  be  in  much  the  same  condition  as  was 
the  ear  of  sweet  corn  just  described. 


ON  STALKS  indication  of  the  Diplodia   fungus  on  the 

dead  stalks  is  the  appearance  of  very  small  dark  col- 
ored specks  under  the  rind.  In  outdoor  conditions  these  may  appear 
during  late  fall  and  winter  but  usually  develop  during  the  spring  and 
summer.  An  examination  of  stalks  in  the  field  on  March  6,  1908, 
revealed  very  few  that  showed  any  developing  pycnidia,  but  in  the 
same  field  and  plat  on  May  14,  1908,  many  stalks  showed  numerous 
developing  spore  cases  just  beneath  the  rind,  few  having  broken 
thru.  (PI.  VI.,  Fig.  1.).  The  stalks  had  been  dragged  and  broken 
off  near  the  ground  and  most  of  the  fertile  portions  were  at  or  near 
the  breaks.  The  pycnidia  are  produced  all  over  the  old  stalks  but  are 
usually  more  abundant  about  the  nodes.  This  condition  is  more  fre- 
quently found  in  two  or  more  year  old  stalks.  There  is  also  a  tendency 
for  them  to  occur  in  vertical  rows.  During  the  summer  the  necks  of 
the  pycnidia  begin  to  break  through  the  rind  of  the  stalks  and  in  favor- 
able weather  conditions  send  out  large  numbers  of  spores.  Pieces  of 
diseased  stalks  one  or  two  years  old  have  been  found  in  July,  August, 
and  September  almost  covered  with  black  tendrils  of  Diplodia  spores 
capable  of  quick  germination.  Apparently  the  spores  are  slightly  coated 
with  a  gelatinous  substance,  as  in  a  protected  place  they  adhere  to- 
gether in  tendrils  for  some  time,  but  immediately  separate  on  the  addi- 
tion of  water.  (PI.  VI.,  Figs.  2  and  3.).  Pieces  of  stalks  almost  three 
years  old  have  been  found  bearing  pycnidia  and  some  few  of  the  spores 
found  in  them  were  capable  of  germination.  These  were  .pretty  badly 
decayed,  however,  and  the  fungus  was  not  in  a  very  active  condition. 


1909]  EAR  ROTS  OF  CORN  75 

This  fungus  has  not  been  found  growing  naturally  on  the  green 
stalks,  although,  as  will  be  further  mentioned,  a  slight  growth  was 
produced  by  artificial  inoculation.  The  green  shanks,  on  the  other 
hand,  are  frequently  found  badly  infected  when  bearing  diseased  ears. 

Old  stalks  may  become  infected,  thru  diseased  ears  and  shanks 
left  on  them  in  the  field,  after  they  are  matured  and  dead.  As  in  the 
ears,  there  seems  to  be  some  growth  of  the  fungus  in  the  stalks  in 
rather  severe  weather  conditions.  Many  stalks  are  no  doubt  infected 
in  the  late  fall,  the  fungus  slowly  spreading  thru  them  and  with  the 
advent  of  spring  weather  developing  its  numerous  pycnidia  and  spores. 
Just  how  long  the  spores  may  retain  their  vitality  in  the  pycnidia  after 
being  formed  is  not  known,  but  that  they  will  germinate  after  remain- 
ing thus  for  six  months  is  shown  by  .the  following  experiment.  During 
August,  1907,  some  infected  pieces  of  old  cornstalks  were  brought  into 
the  laboratory  and  kept  in  a  very  dry  place  during  the  winter.  These 
were  examined  from  time  to  time  and  there  was  no  appearance  of  any 
young  pycnidia.  Most  of  the  old  ones  were  filled  with  spores.  On 
February  25,  1908,  some  pieces  of  these  stalks  were  soaked  over  night 
in  water  and  then  placed  in  a  moist  chamber.  After  a  few  days  long 
tendrils  of  Diplodia  spores  covered  the  surfaces  of  the  stalks.  (PI.  VI., 
Figs.  1,  2,  and  3.).  The  figures  show  one  soaked  and  one  ttnsoaked 
piece  from  the  same  stalk.  A  large  percent  of  these  spores  were  capa- 
ble of  germination.  After  remaining  a  few  days  longer  in  the  moist 
chamber  these  pieces  of  stalks  were  washed  with  a  small  brush,  remov- 
ing all  spores,  and  again  allowed  to  soak  in  water  for  a  few  hours. 
They  were  then  returned  to  the  moist  chamber  with  a  new  piece  of  the 
same  stalk  soaked  for  the  first  time.  The  latter  piece  was  in  a  few 
days  covered  with  the  spore  tendrils,  but  all  others  even  after  weeks 
showed  no  sign  of  exuding  spores  from  old  marked  pycnidia.  A  few 
new  ones  finally  developed  which  produced  spores.  Sections  made  of 
the  old  pycnidia  revealed  only  a  few,  mostly  collapsed  spores  which 
evidently  failed  to  get  out  with  the  others.  This  experiment  together 
with  other  observations  leads  to  the  supposition  and  strong  probability 
that  pycnidia  soon  reach  a  mature  stage  after  which  no  more  spores 
are  produced.  This  explains  the  occurrence  of  so  many  tendrils  of 
spores  on  old  stalks  after  rains  following  dry  weather.  During  the 
dry  period  the  pycnidia  come  to  maturity  and  are  filled  with  spores. 
As  has  been  seen,  moisture  causes  the  expulsion  of  the  spores  and  their 
abundant  appearance  after  rains.  If  the  season  is  rather  moist  thru- 
out,  the  issue  of  spores  is  more  evenly  distributed,  and  danger  is  then 
less  than  when  large  production  occurs  when  the  corn  is  most  sus- 
ceptible. 

Pycnidia  produced  on  corn  stalks  are  fairly  regular  in  size  and 
structure  and  usually  occur  singly.  Sometimes  partitions  separate  the 
interior  into  two  or  more  chambers  which  emit  their  spores  through  a 
common  opening.  Occasionally  one  may  find  several  pycnidia  congre- 
gated together  without  the  presence  of  a  stroma,  but  this  is  rare  on  the 
stalks.  Many  are  vertically  compressed  and  most  of  them  have  a 
thicker  wall  than  those  found  on  the  corn  grains  and  in  cultures.  (PI. 


76  BULLETIN  No.  133  [February, 

X.,  Fig.  1.).  It  will  be  noted  from  the  figure  that  the  wall  of  a  Pyc- 
nidium  is  made  up  of  two  fairly  well  marked  layers  of  tissue,  an  outer, 
composed  of  rather  thick  walled  threads  taking  on  the  nature  of  cells 
by  the  short  joints,  and  an  inner  one  made  of  thinner  walled  cells 
which  form  a  hymenium  or  fruiting  layer. 

Arising  from  this  layer  are  seen  numerous  sphorophores  and  para- 
physes.  The  spores  become  two-celled  before  leaving  the  pycnidium. 
Howard*  states  that  in  the  case  of  Diplodia  cacaoicola,  the  spores  at 
the  time  of  leaving  the  pycnidium  are  greyish  and  unicellular  but  that 
they  soon  become  dark  brown,  the  septum  appearing  at  the  same  time. 

The  mycelium  in  the  stalks  is  mostly  hyalin,  becoming  somewhat 
dark  about  the  pycnidia.  The  beginning  of  a  pycnidium  can  be  seen  in 
section  just  under  the  rind  as  a  rather  closely  matted  and  much 
branched  mass  of  brownish  colored  threads  which  finally  becomes 
almost  black  in  appearance.  The  threads  of  the  mycelium  penetrate 
the  cells  of  the  pith  and  partially  fill  them  and  make  their  way  in  the 
woody  portions  from  one  element  to  another  by  means  of  the  pores. 
(PI.  X.,  Fig.  1.).  In  some  cases  one  can  trace  the  disease  in  the  pith 
by  a  slight  darkening  of  that  tissue,  but  this  is  not  an  infallible  sign  of 
its  presence. 

The  protoplasm  of  the  mycelial  threads  in  the  active,  growing 
condition  is  slightly  granular  and  sometimes  very  much  vacuolated,  but 
in  the  older  and  more  matured  condition  the  threads  are  more  or  less 
filled  with  oil  globules. 

GROWTH  IN  A  large  number  of  cultures  were  made  on  various 

CULTURE  natural  and  artificial  media  with  the  hope  of  inducing 

the  fungus  to  develop  a  perithecial  stage,  but  all  at- 
tempts to  find  such,  either  in  culture  or  in  nature,  have  been  without 
success.  Perhaps  this  stage  has  been  entirely  lost  from  the  life  history 
of  the  fungus  or  it  may  be  that  the  conditions  necessary  for  its  forma- 
tion were  not  found.  Although  many  cultures  were  made  directly 
from  diseased  tissue,  all  comparative  cultures  were  descendants  from 
a  single  spore. 

The  fungus  grows  very  well  on  many  fruit,  vegetable,  and  arti- 
ficial media,  the  amount  of  mycelium  and  number  of  pycnidia  varying 
considerably.  Both  solid  and  liquid  cultures  were  modified  in  various 
ways  as  to  their  reaction  and  the  nature  of  the  carbohydrate  present, 
with  some  striking  results. 

The  media  used  most  extensively  for  propagating  spores  for 
inoculation  work  and  for  maintaining  a  stock  of  pure  cultures  was 
boiled  rice  in  tubes  in  the  proportion  of  2  grams  of  rice  to  8  cc  of  dis- 
tilled water.  This  induced  a  rapid  growth  and  an  abundant  formation 
of  pycnidia  and  spores. 

A  series  of  20  tubes  containing  boiled  vegetables,  grains,  and  nuts 
were  inoculated  and  the  resulting  growths  compared.  A  number  of 
them  proved  excellent  for  the  development  of  mycelium  but  few  were 
suited  for  production  of  spores.  Notes  are  given  as  follows : 

*  Howard,   Albert.      On   the   Diplodia  cacaoicola,    P.  Henri.      A   parasitic   Fungus  on   sugar 
cane  and  cacao  in  the  West  Indies.      Annals  of  Botany  15:686,   1901. 


1909]  EAR  ROTS  OF  CORN  77 

Boiled  turnip. — A  rather  dense,  white  growth,  becoming  grayish  with  age 
and  covering  and  surrounding  most  of  the  slant.  No  pycnidia  developed. 

Boiled  carrot. — Good,  rather  flocculent  growth  surrounded  the  slant.  Pyc- 
nidia rather  sparse. 

Boiled  salsify. — A  very  fair  growth  developed  after  two  weeks  or  more, 
but  no  pycnidia  were  produced. 

Boiled  parsnip. — Excellent  growth  of  white,  rather  cottony  mycelium  sur- 
rounded the  slant.  A  sHght  tinge  of  brown  appeared.  A  good  many  pycnidia 
were  developed. 

Boiled  potato, — Fair,  rather  compact  growth  all  about  the  slant ;  cream  to 
light  brown  with  age.  No  pycnidia  formed. 

Boiled  beet. — Growth  pretty  fair ;  but  mycelium  and  liquid  at  the  bottom  of 
the  tube  very  brown.  No  pycnidia  found. 

Boiled  apple. — Growth  pure  white  and  very  s'ow,  becoming  fair  in  six 
weeks. 

Boiled  macaroni. — Growth  pretty  good ;  white  tinged  with  gray  to  light 
brown  in  patches.  A  good  many  small  pycnidia  formed. 

Boiled  cabbage. — Growth  poor.     No  pycnidia. 

Boiled  orange. — Growth  good ;  white,  becoming  somewhat  gray  with  age. 
A  very  few  small  pycnidia  developed. 

Boiled  onion. — Growth  good;  mostly  white.     Pycnidia  rather  abundant. 

Boiled  Brazil  nuts. — Growth  fair ;  mycelium  tinged  light  brown.  No  pyc- 
nidia. 

Boiled  cccoanut. — Rather  good  growth,  turning  to  dirty  cream,  almost  light 
brown  at  the  lower  portion.  No  pycnidia  developed. 

Boiled  peanuts. — Fair  growth  developed;  white  above,  becoming  light 
brown  with  age.  No  pycnidia. 

Boiled  green  bean  stems. — Growth  fair.     No  pycnidia. 

Boiled  germinated  corn. — Growth  good,  filling  spaces  between  the  grains. 
Very  few  pycnidia. 

Boiled  soaked  corn. — Growth  good ;  white  becoming  slightly  darkened  with 
age.  Pycnidia  rather  numerous. 

Boiled  corn. — Growth  much  like  that  of  the  boiled  soaked  corn  with  more 
pycnidia  present. 

Cccoanut  milk  agar. — Good  growth.     A  good  many  pycnidia  developed. 

Litmus  lactose  agar  (acid). — Growth  fair,  agar  changed  to  blue  at  top,  be- 
coming brownish  later.  Pycnidia  absent. 

Five  cultures  were  made  in  liquid  media  with  Diplodia  spores  from  a  pure 
culture. 

Uschinsky's  fluid*. — In  one  week  a  thin  flocculent  growth  was  present 
thruout  the  liquid  and  a  week  later  most  of  the  growth  was  within  1  cm  of 
the  surface  which  was  covered  by  a  thin  growth.  A  sparse  growth  of  mycelium 
had  extended  8  to  10  mm  up  the  sides  of  the  tube.  The  growth  finally  became 
slightly  more  dense,  showed  a  tinge  of  brown  at  one  place,  and  produced  a  few 
pycnidia  at  the  surface  on  the  sides  of  the  tube. 

Raulin's  fluidt. — In  one  week  a  thin  white  growth  covered  the  surface  of 
the  liquid  and  extended  6  mm  up  the  sides  of  the  tube.  A  slight  submerged 
growth  was  present  near  the  surface.  One  week  later  a  dense  growth  covered 
the  surface  and  the  submerged  portion  for  3  or  4  mm  deep  had  a  beau- 
tiful green  color.  The  aerial  portion  on  the  sides  of  the  tube  showed  alternate 
zones  of  light  cream,  pink,  and  brown.  Later  the  growth  and  the  intensity  of  the 
colors  increased.  The  bright  green  finally  became  a  dirty  green  and  then  almost 
black.  A  few  pycnidia  were  produced. 


78  BULLETIN  No- 133  [February, 

Beef  bouillon. — In  a  week's  time  a  slight  growth  had  developed  thruout 
the  liquid  and  a  rather  dense  layer  of  white  mycelium  covered  the  surface.  In 
two  weeks  the  growth  had  become  more  dense  on  the  surface,  extending  up 
the  sides  of  the  tube  6  to  8  mm  and  thruout  the  liquid  as  a  light  flocculent 
cloud.  The  growth  remained  white  and  but  2  pycnidia  were  found. 

In  a  solution  containing  2  percent  of  Witte's  peptone,  1  percent  dextrose,  1 
percent  maltose,  and  1  percent  mannite,  a  very  dense  growth  had  covered  the 
surface  of  the  liquid  and  a  flocculent  mass  developed  all  thru  it  in  one  week. 
Growth  increased  rather  rapidly,  becoming  more  dense  on  the  surface  and  ex- 
tending well  up  on  the  sides  of  the  tube ;  color  white,  finally  becoming  tinged 
with  brown  in  a  few  places.  The  liquid  below  the  growth  became  deep  orange 
in  color.  Only  a  few  pycnidia  were  produced. 

Distilled  water  with  2  percent  of  Witte's  peptone  and  1  percent  glycerin : — 
In  one  week  the  surface  was  only  partially  covered  with  mycelium  and  but 
little  could  be  seen  thruout  the  liquid.  One  week  later  growth  was  good,  a 
dense  white  mass  covering  the  surface  but  not  extending  far  up  on  the  sides  of 
the  tube.  Slight  growth  in  the  liquid.  Very  few  pycnidia  were  formed. 

Three  series  of  cultures  were  made  relative  to  the 

EFFECTS  OF  ACID         n-  j-         -1  j       11      1-  ,1  xi  i    r 

4-Km  ATTrarrw         effects  of  acid  and  alkali  on  the  growth  and  fruiting 

AJNJJ    A.LK.A.H.N  -,,  ,  r    i         i  •  i    • 

MEDIA  of  the  fungus.  A  number  of  both  organic  and  inor- 

ganic acids  were  used  in  the  two  acid  series  and  one 
alkali,  sodium  carbonate,  in  the  alkalin  series.  The  medium  used  in 
all  tube  cultures  was  boiled  rice,  and  in  plate  cultures  it  was  extract  of 
corn  meal  with  agar. 

The  injurious  effect  of  the  alkali  was  very  apparent  in  cultures 
containing  very  small  amounts  as  three  parts  of  a  normal  solution  to 
one  thousand  of  media  gave  no  growth,  while  slightly  less  amounts 
produced  a  very  weak  mycelium  and  few  pycnidia.  It  should  be  said 
that  boiling  rice  in  the  presence  of  alkali  reduces  the  alkali  proportion- 
ally to  the  amount  present,  and  it  was  found  necessary  to  prepare  an 
extra  series  of  tubes  for  titration  after  sterilization  in  order  to  be  sure 
of  the  reaction  of  the  media  when  inoculated. 

As  a  result  of  the  cultures  in  acid  media  it  was  found  that  of  the 
organic  acids  used  the  most  injurious  were  formic  and  butyric,  mem- 
bers of  the  acetic  series,  while  the  best  growth  and  greatest  develop- 
ment of  pycnidia  took  place  in  the  presence  of  oxalic,  malic,  citric, 
and  tartaric,  members  of  the  hydroxy  acid  group.  At  the  strength  of 
twenty-five  parts  normal  acid  to  one  thousand  of  media  no  growth  took 
place  in  the  presence  of  formic  and  butyric  acids,  while  in  the  presence 
of  acetic,  a  member  of  the  same  group,  there  was  a  pretty  fair  growth 
of  mycelium  tho  very  few  pycnidia.  This  applies  also  to  the  growth 
in  tartaric  and  lactic  acid  cultures.  Of  the  inorganic  acids  used,  hydro- 
chloric, nitric,  and  sulfuric,  the  first  two  were  most  favofable  for 
good  development  of  mycelium,  while  nitric  alone  seemed  to  be  favor- 
able for  the  formation  of  many  pycnidia,  there  being  very  few  to  de- 
velop in  either  of  the  other  two  cultures.  Variation  of  color  appeared 
in  some  of  the  tubes.  In  the  malic  acid  culture  patches  of  cream,  yel- 
low and  orange  to  brown  were  present.  Similar  colors,  but  less  marked, 
appeared  in  the  acetic  and  citric  acid  tubes,  while  that  in  all  others 
was  principally  white  tinged  with  cream  to  gray. 

A  series  of  cultures  was  made  in  poured  plates  for  determining  the 
effects  of  the  acids,  alkalis,  carbohydrates,  and  a  few  other  substances 


1909]  EAR  ROTS  OF  CORN  79 

on  the  production  of  pycnidia.  The  media  to  which  almost  all  the 
above  were  added  was  extract  of  corn  meal  with  agar.  All  acid  cul- 
tures were  made  a  strength  of  -\-2Q,  Fuller's  scale,  and  those  contain- 
ing alkali — 15,  same  scale.*  All  carbohydrates  except  starch  were 
used  5  percent  strength. 

In  two  weeks  the  following  condition  existed  in  the  plates : 

Formic,  acetic,  butyric,  and  oxalic  cultures  had  developed  no 
growth,  while  the  colonies  in  those  containing  malic,  tartaric,  citric, 
and  lactic  acids  covered  the  surface  of  the  plate  and  extended  well  up 
the  sides  with  zonation  clearly  shown.  The  growth  in  standard  agar 
and  standard  gelatin  was  rather  dense  and  covered  most  of  the  plate. 
No  zonation  was  present.  In  the  cultures  containing  glucose,  galactose, 
maltose,  and  cane  sugar  the  growth  was  rather  dense,  especially  at  the 
margin  and  on  the  sides  of  the  plate  which  was  entirely  covered.  In 
litmus-lactose  agar,  Uschinsky's  solution  hardened  with  2  percent 
starch,  and  Fermi's  solution1'  agar  the  growth  was  rather  poor,  particu- 
larly in  the  last  named  medium  where  only  a  small,  thin  colony  devel- 
oped. The  growth  in  the  plates  containing  sodium  and  potassium 
hydroxids  was  very  thin,  irregular,  and  almost  entirely  submerged. 

In  one  week  there  was  in  a  few  cultures — those  containing  glucose, 
galactose,  and  maltose — an  indication  of  forming  pycnidia.  They  rap- 
idly increased  in  another  week  and  at  the  end  of  the  third  week  about 
all  had  formed  that  did  appear.  None  developed  in  standard  agar, 
standard  gelatin,  Fermi's  solution  agar,  potassium  hydroxid,  and 
litmus-lactose  agar;  very  few  in  malic  and  tartaric  acid  cultures,  and 
only  about  50  and  75  in  those  containing  citric  and  lactic  acids.  Three 
developed  in  the  sodium  hydroxid  culture  and  about  40  in  Uschinsky's 
solution  plus  starch.  In  the  check  plate  which  contained  extract  of 
corn  meal  with  agar  the  number  of  pycnidia  was  fairly  large.  The 
cultures  producing  by  far  the  most  pycnidia  were  those  containing  the 
sugars  in  the  order  of  maltose,  galactose,  cane  sugar,  and  glucose. 
Over  200  were  counted  in  one  square  inch  of  surface.  Plate  IX.,  Fig. 
1  is  a  photograph  of  the  galactose  culture. 

It  will  be  noticed  that  most  of  the  pycnidia  develop  near  the  mar- 
gin of  the  plate.  If  only  a  very  few  formed  they  were  almost  invariably 
on  the  sides  of  the  plate  or  at  the  very  margin. 

By  means  of  the  microscope  the  beginning  of  the  pycnidia  can  be 
seen  in  plate  cultures  as  a  small  clump  of  irregularly  branched  and 
darkened  hyphae  which  grow  in  size  quite  rapidly  with  an  increase  in 
color.  Many  of  them  are  entirely  submerged,  form  little  or  no  neck, 
and  discharge  their  spores  into  the  medium  thru  a  more  or  less 
broad  opening  in  the  wall.  It  is  not  unusual,  however,  to  find  per- 
fectly formed  pycnidia  in  such  cultures  but  as  a  rule  the  necks  are 
shorter  than  those  on  the  corn  stalks.  Here,  as  on  the  corn  husks  and 
occasionally  on  the  stalks,  may  be  found  pycnidia  with  the  internal 

*  That  is,  plus  or  minus  so  many  cc  of  normal  sodium  hydrate  to  bring  one  litre  of 
medium  to  the  phenolphthalein  neutral  point. 

t  Fermi's  culture  fluid  is  made  as  follows:  Distilled  water,  1,000  cc;  magnesium  sulfate, 
.2  gram;  acid  potassium  phosphate,  1  gram;  ammonium  phosphate,  10  grams;  glycerin,  45 
grams. 


80  BULLETIN  No.  133  [February, 

cavity  divided  by  partitions  forming  somewhat  irregular  compartments 
communicating  with  each  other  toward  the  orifice.  Sometimes  more 
than  one  orifice  is  present. 

A  number  of  spores  from  seven  of  the  above  cultures  were  meas- 
ured and  the  averages  taken.  The  greatest  variation  was  in  the  length, 
the  width  being  almost  constant.  The  largest  were  in  the  check  plate, 
the  extract  of  corn  meal  with  agar,  and  measured  28.5 X5/x  and  the 
smallest  were  produced  in  the  same  media  plus  lactic  acid  and  meas- 
ured 22.1X5.2/*. 

Mature  spores  germinate  in   from  5  to  8  hours  by 

GERMINATION  ,•  11-  i        r  i      ,1         r    j.t, 

OF  SPORES  sending  out  a  hyalin  hypha  from  one  or  both  of  the 

cells  which  soon  forms  septa  and  branches.  (PL  XL, 
Fig.  3  and  PI.  VII.,  Fig.  2).  The  protoplasm  of  the  germ  tubes  is  at 
first  finely  granular,  but  as  they  begin  to  grow  more  rapidly  it  becomes 
vacuolated. 

Almost  all  germinations  were  made  in  Van  Tieghem  cells  three- 
fourths  Inch  in  diameter,  using  various  liquid  media  and  spores  from 
different  sources  depending  upon  the  nature  of  the  test.  Within  three 
or  four  days  a  tangled  skein  of  mycelium  forms  and  fusion  of  hyphae 
is  not  uncommon.  There  may  be  seen  here  and  there  small  dark 
specks,  the  beginning  of  pycnidia.  Cell  cultures  offer  a  good  means 
of  studying  the  first  processes  in  such  formations  which  usually  start 
with  hyphae  in  direct  contact  with  the  cover  glass.  These  first  send 
out  short,  thickened  branches  which  become  gradually  darkened  and 
usually  contain  a  small,  circular,  light  spot.  (PL  XL,  Fig.  4).  They 
increase  in  number  and  complexity  until  a  sort  of  cellular  tissue  results 
as  has  already  been  described. 

In  Uschinsky's  fluid  no  germination  had  taken  place  in  5  hours ; 
two-fifths  of  the  spores  had  germinated  in  9  hours,  and  nine-tenths  in 
70  hours,  at  which  time  the  hyphae  were  considerably  branched. 

In  Raulin's  fluid  about  8  percent  were  germinating  in  70  hours. 
The  germ  tubes  were  short  and  unbranched. 

One-third  of  the  spores  had  germinated  in  beef  bouillon  within  9 
hours,  three-fourths  in  22  hours,  and  practically  all  in  70  hours. 
Pycnidia  had  begun  to  form  in  several  places. 

In  a  solution  containing  2  percent  of  Witte's  peptone,  1  percent 
dextrose,  1  percent  maltose,  and  1  percent  mannite,  germination  began 
in  5  hours;  in  9  hours  about  half,  and  in  70  hours  nearly  all  had  ger- 
minated. Pycnidial  formations  had  begun. 

In  a  solution  containing  2  percent  of  Witte's  peptone,  and  1  per- 
cent of  glycerin  only  a  few  spores  had  germinated  in  9  hours.  In  22 
hours  about  one-third  had  germinated. 

No  germination  took  place  in  distilled  water. 

The  following  tests  were  made  January  1,  1908,  to  determine  the 
viability  -of  spores  of  different  ages.  Seven  cultures  were  made  in 
corn  meal  extract  with  spores  from  the  following  sources : 

No.  1.     Boiled  rice  tube  culture  19  days  old. 
No.  2.     Boiled  rice  tube  culture  51  days  old. 


1909] 


EAR  ROTS  OF  CORN 


81 


No.  3.  Surface  of  pieces  of  husk  which  had  been  in  a  test  tube  almost  5 
months. 

No.  4.  A  diseased  ear  of  corn  of  the  1907  crop,  which  had  been  in  the 
laboratory  about  3  weeks. 

No.  5.  An  old  corn  stalk  brought  into  the  laboratory  November  15,  1907. 

No.  6.  A  specimen  of  corn  sent  to  the  laboratory  in  March,  1907. 

No.  7.  Corn  specimens  collected  January  1,   1907. 

The  results  are  shown  by  the  figures  tabulated  below : 


Date 

No. 

Medium 

Started 

Percent  germinated  in 

v 

5  hrs 

22  hrs. 

30  hrs. 

46  hrs. 

64  hrs. 

cornmeal 

Jan.  27 

1 

extract 

11:30  a.  m. 

60 

90 

95 

95 

95- 

2 

10 

90 

90 

95 

95 

3 

0 

1 

.       1 

1 

1 

4 

8 

33 

40 

40 

45 

5 

0 

40 

43 

45 

45 

6 

0 

0 

0 

0 

0 

7 

0 

0 

0 

0 

0 

January  29,  1908,  Diplodia  spores  were  taken  from  an  old  piece  of 
corn  stalk  which  had  been  lying  outside  the  building  and  exposed  to 
the  weather  since  August,  1908,  and  sown  in  corn  meal  extract  in  a 
Van  Tieghem  cell.  In  48  hours  10  to  12  percent,  and  in  96  hours  15 
percent  had  germinated. 

On  February  3,  four  cell  cultures  were  made  with  Diplodia  spores 
from  pieces  of  old  diseased  corn  stalks  which  had  been  in  the  labora- 
tory since  August,  1907,  and  which  5  days  previous  had  been  soaked 
24  hours  in  water  and  then  placed  in  a  moist  chamber  where  they  pro- 
duced numerous  tendrils  of  spores  some  of  which  were  used  in  the 
test.  The  medium  used  was  corn  meal  extract  and  the  temperature 
was  26°  C.  to  28°  C. 

In  5  hours  No.  1  showed  a  germination  of  80  percent;  No.  2,  85 
percent ;  No.  3,  92  percent ;  and  No.  4,  90  percent.  In  23  hours  No.  1 
had  germinated  95  percent ;  No.  2  about  95  percent ;  and  No.  4,  92  per- 
cent, j  ' 
The  field  in  which  this  experiment  was  carried  on  is 
situated  on  a  rather  high  knoll  on  the  University  south 
farm.  In  1906  it  produced  a  crop  of  corn,  60  bushels 
per  acre,  10  percent  of  which  was  destroyed  by  rot. 
The  stalks  were  not  cut  nor  were  they  pastured.  In  July,  1907,  the 
south  half  of  the  field  was  sowed  to  cow  peas,  the  north  half  having 
been  seeded  to  clover  earlier  in  the  season.  Numerous  pieces  of  old 
corn  stalks,  some  at  least  two  years  old,  were  scattered  about  on  the 
surface  of  the  ground  and,  being  more  or  less  protected  by  the  grow- 
ing cow  peas,  were  producing  in  many  cases  an  abundance  of  Diplodia 
spores.  Early  in  September  the  cow  peas  were  cut  and  oats  were 
sowed  as  a  cover  crop  to  the  young  apple  trees  to  which  the  field  was 
planted. 

On  September  17,  three  stakes  were  set  up  in  the  field,  one  on  the 
north  edge  of  the  recently  plowed  south  half,  and  the  other  two  toward 


DISTRIBUTION 
OF   SPOKES 
BY  WIND 


82  BULLETIN  No.  133  [February, 

the  north  edge  of  the  clover  field.  The  entire  field  was  about  25  rods 
wide.  To  each  of  these  stakes,  5^2  feet  long  and  driven  8  to  10  inches 
into  the  ground,  were  fastened  2  glass  plates  6l/2  x  8j/2  inches,  one  at 
the  fop,  the  other  2  feet  below.  The  plates  which  faced  northeast  and 
southwest  were  smeared  on  both  sides  with  glycerin  and  alcohol.  The 
surface  of  the  ground  was  rather  dry  and  a  brisk  wind  was  blowing 
from  the  southwest.  After  48  hours  the  glass  plates  were  removed 
and  new  ones  similarly  treated  put  in  their  places.  The  glycerin  and 
contents  was  washed  from  the  sides  of  each  plate  into  separate  watch 
glasses  with  95  percent  alcohol,  and  after  considerable  evaporation  the 
spores  were  counted.  It  is  quite  probable  that  many  of  the  spores  were 
not  washed  from  the  plate  by  this  method  and  that  the  results  shown 
below,  although  strongly  convincing,  represent  only  part  of  the  true 
condition. 

Stake  No.  1.     On  plowed  ground.  Upper  plate,    65  Diplodia  spores. 

Lower  plate,  400  (approximately)  spores. 
Stake  No.  2.    About    the    middle    of     Upper  plate,  50  spores. 

clover  field.  Lower  plate,  75  spores. 

Stake  No.  3.     North    side    of    clover     Upper  plate,  40  spores. 

field.  Lower  plate,  about  40  spores. 

The  second  set  of  plates  placed  on  the  stakes  were  not  considered 
further,  but  on  October  1,  1907,  4  microscopic  object  slides,  3  inches 
long  by  1  inch  wide,  were  placed  on  two  of  the  above  mentioned  stakes, 
two  on  each,  and  the  south  surface  of  each  smeared  with  glycerin  and 
alcohol.  These  could  be  examined  under  the  microscope  directly  and 
more  accurate  results  could  be  obtained. 

After  3  days,  during  which  time  a  hard  rain  occurred,  the  slides 
were  removed  and  a  new  set  substituted,  two  on  each  of  the  three 
stakes.  The  count  on  the  4  slides  was  as  follows : 

Stake  No    1       Upper  slide,  25  spores. 
Lower  slide,  33  spores. 

Stake  Nn    2       Upper  slide,  2  spores. 
™'  Z-      Lower  slide,  9  spores. 

On  October  5,  after  remaining  on  the  stake  24  hours  the  6  micro- 
scopic slides  were  removed  and  the  counts  made.  They  were  as  fol- 
lows: 

Stake  No    1       Upper  slide,  24  spores. 
No<  L      Lower  slide,  36  spores. 

Stake  No   2       Upper  slide,   22  spores. 

Lower  slide,  250  spores.     A  tendril  was  present. 

Stake  No    1       Upper  slide,    8  spores. 
Lower  slide,  26  spores. 

The  following  experiment  was  made  to  test  whether  the  Diplodia 
spores  could  be  caught  from  the  air  at  some  considerable  distances 
from  the  infected  field.  Adjacent  to  this  field  on  the  north  is  a  golf 
field  which  offered  an  excellent  opportunity  for  making  such  a  test  as 
it  was  very  clean  and  free  from  trash,  and  one  could  feel  quite  certain 
that  most  of  the  spores  obtained  must  have  come  from  the  field  above 
mentioned.  There  was  a  field  of  corn  to  the  west  of  the  golf  field 
but  the  stakes  were  kept  at  least  as  far  from  it  as  from  the  infected 


1909]  EAR  ROTS  OF  CORN  83 

field  to  the  south.  Stake  No.  1,  bearing  two  glass  object  slides,  was  set 
up  in^the  golf  field  50  yards  north  of  the  north  edge  of  the  clover  field 
with  the  smeared  side  of  the  glass  slides  facing  the  south. 

Stake  No.  2  was  similarly  set  up  75  yards  from  the  same  field, 
but  on  slightly  higher  ground. 

Stake  No.  3  was  put  150  yards  away.  This  experiment  was  started 
October  10,  1907. 

After  4  days,  October  14,  the  above  mentioned  slides  were  re- 
moved and  the  counts  made.  They  were  as  follows : 

Stake  No.  1,-SO  yards  from  infected  field         Upper  slide,  28  spores. 

Lower  slide,  37  spores. 
Stake  No.  2,  75  yards  from  infected  field  Upper  slide,  11  spores. 

Lower  slide,  6  spores. 
Stake  No.  3,  150  yards  from  infected  field  Upper  slide,  38  spores. 

Lower  slide,  47  spores. 

On  October  18  at  8  a.  m.,  the  above  experiment  was  repeated  by 
using  greater  distances  in  the  same  field.  Stake  No.  1  was  placed  150 
yards,  No.  2,  250  yards,  and  No.  3,  350  yards  from  the  infected  field. 
In  addition  to  the  two  glass  slides  used  on  each  stake  as  stated  above, 
a  third  was  placed  at  the  top  of  e'ach  stake  facing  the  corn  field  to  the 
west.  This  field  was  the  same  distance  from  each  stake — about  150 
yards.  All  surfaces  of  the  slides  facing  the  south  and  west  were 
smeared  with  glycerin  and  alcohol. 

The  test  continued  4  days  during  which  time  no  rain  fell.  On 
October  22,  the  slides  were  removed  and  sometime  later  the  count  was 
made,  the  slides  in  the  meantime  being  carefully  protected.  The  re- 
sulting count  was  as  follows : 

Slide  1  facing  corn  field,          11  spores. 

Stake  No.  1 — 150  yds.  Slide  2  facing  infected  field.  12  spores 
Slide  3  facing  infected  field,  6  spores. 
Slide  1  facing  corn  field,  4  spores. 

Stake  No.  2— 250  yds.  Slide  2  facing  infected  field.  5  spores 
Slide  3  facing  infected  field,  7  spores 
Slide  1  facing  corn  field,  5  spores. 

Stake  No.  3 — 350yds.  Slide  2  facing  infected  field.  6  spores. 
Slide  3  facing  infected  field,  14  spores. 

These  results  entirely  confirmed  the  supposition  of  the  transmis- 
sion of  Diplodia  spores  by  the  wind  and  furnished  the  means  for  the 
explanation  of  several  peculiar  things  in  reference  to  the  distribution 
of  the  disease. 

TwnpTTT  ATTHV         It  was  now  desired  to  perform  some  infection  experi- 

1IV  UL/ UJ-.A  J.1UJN  •"•'"<  /-/•      r  1  1  T        TT        1    • 

EXPERIMENTS        having  been  cut  off  from  the  sporophore.     In  Uschin- 
sky's   fluid   90  percent   germinated   in   24  hours   and 
oculations  were  made  as  follows : 
1.     On  sweet  corn. 

a.  On  August  10,  1907,  a  number  of  well  .selected  ears  whose 
silk  was  just  beginning  to  dry  were  inoculated  with  spores  from  a  rice 
tube  culture  forty  days  old,  by  inserting  the  spores  under  the  outer 
husk  at  the  base  of  the  ear  in  some  cases,  and  ;n  others  by  placing  them 


84  BULLETIN  No.  133  [February, 

well  down  into  the  silk  at  the  tip.     The  same  thing  was  carried  out  in 
duplicate  using  exuded  spores  from  an  old  diseased  corn  stalk. 

Within  five  or  six  days  the  success  of  the  infections  was  apparent 
from  the  small  but  striking  spots  of  pale  yellowish  green  that  appeared. 
These  increased  rapidly  in  size,  changing  to  the  characteristic  brown 
color  along  the  margins.  The  disease  in  the  majority  of  cases  pro- 
gressed somewhat  more  rapidly  in  the  ears  inoculated  at  the  base  but 
no  apparent  difference  could  be  detected  in  the  final  effect.  Those  in- 
oculated with  spores  from  pure  cultures  were  in  appearance  in  no  way 
unlike  those  that  were  inoculated  with  spores  from  the  old  stalks,  the 
disease  in  all  progressing  at  the  same  rate  and  showing  the  same  symp- 
toms. On  August  27,  seventeen  days  after  inoculation,  pycnidia  could 
be  seen  developing  on  some  of  the  ears.  From  this  time  on  the  ears 
proper,  kernels  and  cob,  became  rapidly  involved  and  more  or  less  cov- 
ered with  the  white  mycelium. 

September  3,  a  stalk  bearing  two  diseased  ears  was  cut  and  after 
remaining  in  the  laboratory  seven  days  the  upper  of  the  two  ears  was 
photographed.  (PL  IV.,  Fig.  2).  The  great  number  of  pycnidia  can 
be  seen  as  black  masses  towards  the  base  of  each  ear. 

b.  On  August  19  some  ears  of  sweet  corn  in  the  same  plot  as 
above  were  sprayed  with  spores  in  suspension  and  others  were  inocu- 
lated by  inserting  spores  in  the  shank  a  few  inches  below  the  base  of 
the  ear.  Three  of  the  sprayed  ears  developed  rot,  7  did  not,  while  but 
1  of  the  10  inoculated  in  the  shank  was  successful.  (PL  IV.,  Fig.  1). 

2.     On  field  corn. 

At  intervals  from  August  14,  1908,  to  September  13,  1908,  inocu- 
lations were  made  in  ears,  shanks,  and  stalks  of  field  corn  with  spores 
from  both  pure  cultures  and  old  diseased  stalks.  Ears  were  inoculated 
in  the  silk,  at  the  base,  and  by  spraying  them  with  a  suspension  of 
spores  in  water.  Spores  were  inserted  into  wounds  made  in  the  stalks 
in  different  places  by  means  of  .1  knife  or  needle  after  which  a  few 
drops  of  distilled  water  were  added. 

At  the  beginning  of  the  experiment  the  corn  was  just  silking  out 
well  and  showed  no  signs  of  drying  whatever,  while  on  September  13, 
the  date  when  the  last  inoculations  were  made,  some  of  the  husks 
showed  signs  of  maturing  and  the  grains  were  already  quite  firm. 
From  40  to  60  ears  were  used  for  each  method  of  inoculation  and  a 
similar  number  were  always  left  as  checks. 

Of  all  the  inoculations  made  the  most  successful  in  all  the  series 
were  those  with  spores  placed  in  the  silk  and  under  the  outer  husk  at 
the  base  of  the  ears,  the  former  giving  a  higher  percent  of  successful 
inoculations  than  the  latter. 

Of  those  inoculated  August  14  from  a  pure  culture,  16  percent  of 
those  receiving  spores  in  the  base  were  successful,  while  59  percent  of 
the  silk  inoculations  developed  typical  cases  of  the  disease.  The  per- 
cents  of  diseased  ears  resulting  from  the  other  methods  were  small ; 
3.3  from  spraying,  3.1  from  inoculations  made  in  the  stalk  just  below 
the  attachment  of  the  shank,  and  1.5  percent  from  the  checks. 


1909]  EAR  ROTS  OF  CORN  85 

The  percent  of  disease  was  lower  in  all  cases  when  spores  from 
exuded  tendrils  on  old  stalks  were  used.  Of  those  inoculated  on 
August  16  with  such  spores  the  results  were  as  follows :  In  the  silk 
27  percent,  in  the  base  14,  by  spraying  3.6,  and  in  the  stalks  1.8  percent, 
which  last  was  just  about  the  same  amount  of  disease  as  developed  in 
the  checks. 

The  highest  percents  of  diseased  ears  obtained  were  the  result  of 
inoculations  made  on  August  31,  as  previously  stated,  when  the  corn 
was  still  in  the  thick-milk  stage.  80  percent  of  silk-inoculated  ears 
produced  the  disease,  71.7  percent  of  those  inoculated  at  the  base  and 
48  percent  so  treated  in  the  shanks  were  successful,  while  but  22  per- 
cent of  the  sprayed  ears  showed  any  signs  of  infection.  All  later  inoc- 
ulations altho  fairly  successful  produced  smaller  percents  of  the  disease 
than  the  others. 

Microscopical  examination  of  the  tissue  of  inoculated  stalks 
showed  some  development,  mostly  slight,  in  a  number  of  cases.  In 
one  case  the  pith  was  browned  below  and  above  the  wound,  together 
a  distance  of  three  feet,  and  tubes  of  boiled  rice  inoculated  with  bits  of 
the  tissue  developed  the  Diplodia  fungus.  There  was  no  direct  evi- 
dence obtained  that  the  infected  ears  on  such  stalks  were  a  result  of  the 
inoculations  made. 

A  number  of  inoculations  made  on  stalks  and  leaf  sheaths  by 
merely  applying  spores  to  the  uninjured  surface  of  each  and  in  slight 
wounds  made  by  scratching  with  a  needle  were  entirely  unsuccessful. 

INOCULATIONS  ®n  September  5,  1907,  several  stalks  of  sorghum 
IN  OTHER  PLANTS  were  inoculated  about  two  feet  from  the  ground  with 
Diplodia  spores  in  wounds  made  with  a  pen  knife. 
Five  weeks  later  the  stalks  were  harvested,  split  open  and  examinations 
made.  In  most  cases  there  was  about  the  wound  in  the  pith  signs  of 
infection.  The  tissue  had  a  deep  purplish  red  color  and  fermentive 
odor  was  evident.  Mycelium  of  some  kind  was  present  in  all  cases 
but  there  was  no  assurance  as  to  its  being  of  the  Diplodia  fungus.  The 
discoloration  in  one  specimen  extended  about  14  inches  above  and  3 
inches  below  the  point  of  infection.  With  pieces  of  this  diseased  tissue 
2  tubes  of  boiled  rice  were  inoculated,  one  piece  from  near  the  wound 
and  the  other  from  the  portion  farthest  away.  Both  tubes  developed 
impure  cultures  of  the  Diplodia  fungus  and  pycnidia  were  produced. 
Of  the  several  other  plants  inoculated  none  became  infected. 

SPECIES  OF  FUSARIUM. 

The  species  of  Fusarium  found  upon  developing  ears  of  corn  seem 
to  be  undescribed,  notwithstanding  the  number  of  forms  which  have 
from  time  to  time  been  described,  and  the  very  considerable  attention 
that  has  recently  been  given  to  the  group  on  the  part  of  plant  patholo- 
gists  and  other  botanists.  There  are  evidently  three  different  kinds  on 
corn  which  are  sufficiently  distinct  to  be  considered  separate  species. 
One  of  these  has  been  studied  at  length  and  the  others  enough  to  per- 
mit the  descriptions  which  follow  below.  It  has  not  been  considered 


86       '  BULLETIN  No.  133  [February, 

best,  however,  to  give  names  to  these  fungi  in  this  publication,  but 
simply  refer  to  them  by  number.  They  are  therefore  designated 
Fusarium  I.,  Fusarium  II.,  and  Fusarium  III.  It  should  be  said  that 
the  field  loss  by  all  these  does  not  appear  to  amount  to  more  than  about 
9  percent  of  that  due  to  Diplodia,  tho  they  are  parasites  in  the  same 
sense  as  the  latter.  They  do  cause,  independently  of  the  Diplodia 
fungus  and  of  each  other,  a  variable  percentage  of  the  destruction  wit- 
nessed. 

Fusarium  I. 

ON  THE  EASS  ^s  t^ie  ^ungus  grows  on  the  ears  of  corn  it  usually 
produces  a  rather  dense,  felty  mass  of  white  mycelium 
which  extends  between  the  kernels  to  the  cob  causing  it  to  become  more 
or  less  diseased.  (PI.  IT.,  Fig.  1).  The  threads  of  the  mycelium  can 
be  detected  microscopically  all  through  the  diseased  grains,  corroding 
the  starch  and  destroying  the  germs. 

In  the  earlier  stages  of  development  on  the  ears  the  oval  or  pear 
shaped  spores  are  rare  but  in  the  old  advanced  cases  they  are  more  or 
less  numerous.  Two  types  of  spores  are  produced,  microconidia,  small, 
obovate,  single-celled  spores,  and  macroconidia,  larger,  two  to  four 
celled  ones.  The  latter  are  not  commonly  found  in  large  numbers  on 
the  ears  or  in  culture.  In  but  one  case  were  they  found  in  sufficient 
abundance  to  produce  a  pink  color  and  then  on  a  dried  embryo  ear 
(that  is,  an  undeveloped  branch  or  ear  generally  found  in  the  leaf- 
sheath  next  below  that  from  which  the  principal  ear  issues)  which  had 
been  destroyed  by  the  fungus.  (PL  XI.,  Fig.  15).  Some  of  both 
forms  as  taken  from  an  ear  of  corn  are  seen  in  Plate  XL,  Figure  12. 

OK  THE  STALKS  Very  little  is  known  as  to  the  life  history  of  the  fun- 
gus on  corn  stalks.  That  it  does  occur  there  is  cer- 
tain from  the  fact  that  a  culture  made  in  a  tube  of  boiled  rice  with 
discolored  pith  from  a  stalk  near  a  node  gave  an  almost  pure  culture  of 
the  fungus.  It  has  been  found  causing  rots  of  embryo  ears  and  doubt- 
less the  mycelium  penetrates  the  stalk  as  a  result,  as  in  the  above  men- 
tioned cas"e. 

In  culture  the  fungus  shows  a  vigorous  vegetative  ac- 
tivity  and  develops  a  large  amount  of  a  white,  rather 
dense  mycelium  on  most  suitable  media. 
On  a  plate  of  asparagin-glucose  agar,  a  centrally  located  colony 
grew  to  be  25  inches  in  diameter  in  less  than  4  days — the  amount  of 
aerial  growth  increasing  with  age  until  scarcity  of  moisture  checked  it. 
The  amount  of  such  growth  depends  greatly  on  the  moisture  content 
of  the  air  as  is  seen  in  tubes  of  rice  with  various  amounts  of  water 
present.  Under  favorable  conditions  it  will  grow  to  a  height  of  20 
mm  above  the  surface  of  the  media. 

The  mycelium  is  made  up  of  large  and  small  filaments  interwoven 
and  frequently  much  coalesced,  the  latter  depending  largely  on  the  kind 
of  media  used,  and  when  occurring  to  any  considerable  extent  the 
growth  has  a  stringy  or  ropy  appearance.  The  large  filaments  are  a 


1909]  EAR  ROTS  OF  CORN  87 

sign  of  vigorous,  active  growth  and  vary  in  size  from  6  to  10/x 
in  diameter.  Lack  of  moisture  in  a  culture  aids  in  bringing  about  the 
formation  of  the  small  type  of  hyphae  and  a  production  of  conidia. 
These  small  filaments  vary  in  size  from  2  to  4jn  in  diameter  and  hence 
are  small  in  comparison  with  the  larger  ones. 

In  a  young  culture  the  hyphae  are  usually  filled  with  granular 
protoplasm,  becoming  during  the  growing  period  very  much  vacuo- 
lated.  In  certain  old  cultures  with  the  ceasing  of  the  vegetative  activ- 
ities, especially  on  a  very  starchy  media,  the  minute  fatty  drops,  which 
give  the  granular  or  turbid  appearance  to  the  protoplasm  during  the 
active  growing  period,  seem  to  collect  into  large,  strongly  refringent 
drops  and  occupy  the  greater  part  of  the  cells. 

As  seen  under  the  microscope,  the  microconidia  are  colorless,  obo- 
vate  to  pyriform,  and  vary  in  size,  sometimes  considerably,  with  the 
media  used.  They  are  produced  terminally  on  simple  or  much  branched 
sporophores.  (PI.  XL,  Fig.  13).  The  end  of  a  terminal  hypha,  or 
more  frequently  a  lateral  branch,  is  cut  off  from  the  remaining  portion 
by  a  rather  narrow  constriction.  One  after  another  is  thus  formed 
until  a  clump  of  spores  surrounds  the  tip  of  the  branch. 

The  macroconidia  vary  much  in  form  and  size,  ranging  from  10- 
25X4-8/*,  the  average  being  about  18-22X5-6^.  They  are  usually 
slightly  curved  and  somewhat  constricted  at  the  septa.  (PI.  XL,  Fig. 
15).  In  cultures  they  are  usually  rounded  at  the  distal  end  and  taper 
toward  the  bluntly  acute,  proximal  end. 

This  type  of  spore  is  formed  in  culture  in  very  much  the  same 
way  as  the  smaller  form  and  sometimes  on  the  same  hypha.  This  was 
observed  in  both  prune  juice  and  Uschinsky's  fluid.  (PI.  XL,  Fig. 
16).  So  far  as  observations  in  this  connection  could  be  made  the 
sporophores  producing  the  large  and  small  spores  are  little  if  any  dif- 
ferent in  appearance.  In  both  cases  there  is  a  slightly  swollen  portion 
in  the  middle  of  the  branch  and  a  slight  constriction  at  the  point  of 
attachment  to  the  mycelial  filament. 

GERMINATION  Both  types  of  spores  germinate  very  readily  in  many 
different  nutrient  solutions.  In  standard  beef  bouillon 
germination  began  in  3  hours,  and  2  hours  later  one-third  of  the  spores 
produced  germ  tubes.  In  9  hours  all  had  produced  hyalin  germ  tubes, 
some  of  which  were  quite  long.  In  22  hours  many  interwoven 
branches  had  formed.  At  the  end  of  48  hours  no  spores  had  formed. 
Other  tests  were  made  in  Raulin's  fluid,  Uschinsky's  fluid,  com- 
binations of  Witte's  peptone,  glycerin,  etc.,  prune  juice,  and  distilled 
water.  Raulin's  fluid  induced  fair  germination,  but  little  growth  of 
the  hyphae  took  place.  Prune  juice  proved  a  rather  favorable  medium 
but  not  so  good  as  Uschinsky's  fluid.  In  this  solution  germination  was 
very  good  but  the  germ  tubes  never  became  very  long.  In  48  hours 
both  kinds  of  spores  were  being  produced.  In  no  other  medium  were 
the  large  type  of  spores  produced  in  such  abundance.  In  distilled 
water  both  germination  and  growth  were  poor. 


BULLETIN  No.  133  [February, 

GROWTH  ON  fact  that  a  few  cases  are  on  record  of  inducing 

VARIOUS  MEDIA  the  formation  of  perithecia  from  the  conidial  fructi- 
fication of  some  Hypocreaceous  fungi  led  to  the  modi- 
fication of  media,  both  natural  and  synthetic,  in  various  ways  in  an 
attempt  to  find  such  a  stage  in  the  life  history  of  this  organism.  How- 
ever, no  indication  of  perithecia  or  any  other  form  of  fruit  than  those 
described  developed. 

The  fungus  grows  well  on  many  fruit,  vegetable,  and  grain  media 
made  by  boiling  in  certain  amounts  of  distilled  water.  At  all  times 
this  organism  was-  distinguishable  from  other  Fusariums  studied  by 
the  large  amount  of  at  first  pure  white  mycelium.  On  sweet  potato, 
carrot,  salsify,  parsnip,  and  rice,  the  growth  rises  15  to  20  mm  above 
the  surface  of  the  medium  in  a  few  days.  Poor  growths  take  place  on 
apple,  raw  potato,  -tapioca,  prunes,  and  cabbage.  Macroconidia  are 
sparingly  produced  on  some  of  the  media  but  microconidia  are  always 
present  and  usually  in  abundance. 

That  the  production  of  spores  is  largely  influenced  by  external 
conditions — insufficient  nourishment,  lack  of  moisture,  high  tempera- 
ture, and  reaction  of  the  medium — was  strongly  brought  out  in  the 
many  cultures  made. 

The  three  first  named  conditions  favor  the  production  of  spores, 
while  the  last  may  be  so  controlled  as  to  be  either  favorable  or  un- 
favorable. Extremes  in  acids  and  alkalin  reactions  retard  while  those 
of  less  degree,  such  as  favor  good  growth,  are  more  or  less  favorable 
to  the  production  of  spores. 

The  effect  of  alkalis  in  cultures  are  more  injurious  than  acids. 
Of  the  three  alkalis  used — potassium  hydroxid,  sodium  hydroxid,  and 
sodium  carbonate — the  two  former  are  the  most  injurious.  Growth 
is  retarded  by  the  presence  of  acid  above  certain  small  amounts,  the 
strength  depending  largely  on  the  kind  used.  Liquid  media  proved  to 
be  the  most  useful  in  determining  such  effects.  Acids  of  the  acetic 
series  were  found  to  be  the  most  injurious,  growth  refusing  to  take 
place  in  strengths  above  -(-6.25  in  a  liquid  medium,  while  those  of  the 
hydroxy  acid  group  are  least  so,  permitting  growths  in  strengths  of 
-j-25,  and  in  some  cases  stronger. 

On  most  media  used  a  pigment  varying  in  color  from  salmon  to 
purple  appeared  in  time,  and  was  found  to  be  artificially  more  or  less 
controllable.  It  is  retarded  by  weak  solutions  of  alkalis  and  stronger 
solutions  of  acids,  as  a  rule,  altho  weak  strengths  of  malic,  tartaric, 
citric,  and  lactic  acids  do  under  favorable  conditions  intensify  colors, 
especially  the  salmon,  pink,  and  red.  High  temperature,  on  the  other 
hand.  29°C  to  30°C,  favors  the  production  of  color,  particularly  the 
reddish  purple  hues  produced  in  the  substratum.  When  a  still  higher 
temperature,  as  35°C  to  37°C,  is  used  growth  is  seriously  retarded  and 
sometimes  the  fungus  is  killed.  Color  formation  is  largely  favored 
by  light,  the  salmon  color  increasing  rapidly  in  the  aerial  mycelium  of 
cultures  kept  in  the  dark  for  a  time  and  then  submitted  to  the  action 
of  the  light. 


1909]  EAR  ROTS  OF  CORN  89 

Fusarium  II. 

GROWTH  ON  The  diseased  portion  of  ears  infected  with  this  organ- 

THE  CORN  ism,   as  previously  stated,  have  a  deep  pink  to   red 

color  due  to  the  pigment  produced  in  the  hyphae  of 
the  fungus.  When  the  husks  are  removed  the  color  is  bright,  espe- 
cially in  the  most  active  stage  of  the  organism.  A  microscopical  ex- 
amination reveals  that  the  pigment  is  more  or  less  irregularly  distrib- 
uted in  the  rather  large  mycelial  threads,  some  cells  being  entirely 
without  it. 

Branching  is  moderately  profuse  and  hyphal  swellings  are  not 
rare.  As  yet  no  spores  of  any  kind  have  been  found  on  diseased  ears, 
and  for  a  time  the  organism  was  considered  sterile  and  so  reported  at 
the  Chicago  meeting  of  the  American  Association  for  the  Advancement 
of  Science,  January  1,  1908.*  Latert  however,  spores  were  produced 
in  culture,  which  placed  the  fungus  in  the  genus  Fusarium.  The  felty 
mass  of  mycelium  permeates  the  inner  husks  and  silk  and  holds  them 
firmly  to  the  ear.  (PI.  II.,  Fig.  2).  With  age  the  red  color  fades. 
The  kernels  are  brittle  and  the  starchy  contents  is  very  powdery  and 
considerably  corroded  by  the  action  of  the  hyphae  which  permeate  all 
portions  of  the  grain.  (PI.  XL,  Fig.  7). 

GROWTH  IN  Fusarium  II.  was  usually  grown  in  petri  dishes  on 

CULTURE  various  media  and  on  modifications  of  the  same  ones 

to  induce  the  formation  of  the  reproductive  bodies. 
All  stock  cultures  were  made  on  boiled  rice  in  test  tubes  and  transfers 
of  mycelium  were  made  from  these  to  the  plates.  A  pure  culture  was 
first  obtained  from  the  interior  of  a  sterilized  diseased  kernel  of  corn. 

A  series  of  cultures  was  carried  on  in  plates  duplicate  to  those 
used  with  Diplodia,  the  principal  medium  being  extract  of  corn  meal 
agar,  to  which  various  amounts  of  acids,  alkalis,  and  carbohydrates 
were  added. 

The  fungus  grew  rapidly  on  a  number  of  these  and  in  several 
cases  soon  produced  the  characteristic  purplish-red  color,  but  of  more 
brilliant  hues  than  occur  on  the  infected  corn. 

In  4  days  some  growth  had  developed  on  all  plates  except  the  one 
containing  formic  acid  -{-20  and  on  a  starch  medium  containing  Uschin- 
sky's  solution.  The  colonies  on  the  media  containing  various  sugars 
showed  more  rapid  development  and,  at  first,  more  color.  Density  of 
growth,  however,  was  more  pronounced  in  the  plates  containing  tar- 
taric,  citric,  and  lactic  acids,  where  branching  was  abundant  and  the 
colors  white  to  orange.  The  colony  in  glucose  culture  was  2.5  inches 
in  diameter  at  this  time,  the  margin  having  a  deep  pink  color  while  that 
of  the  central  area  was  a  bright  red.  Bladder-like  swellings  which 
gave  rise  to  from  1  to  12  finger-like  branches  were  numerous  in  the 
substratum.  This  condition  existed  to  a  greater  or  less  extent  in  all 
plate  cultures  containing  sugar. 

Four  days  later,  or  8  days  after  inoculation,  there  was  no  apparent 
growth  in  the  cultures  containing  formic,  acetic,  butyric,  and  oxalic 

*  Barrett,    lames   '!'.,    Science   N.    S.    27:    212. 


90  BULLETIN  No.  133  [February, 

acids,  while  in  all  others  a  more  or  less  rapid  increase  in  the  amount  of 
both  submerged  and  aerial  mycelium  had  taken  place.  The  pigment 
in  the  malic,  tartaric,  citric,  and  lactic  acid  cultures  varied  in  color  from 
brilliant  yellow  to  purplish  red.  Finally  the  resulting  color  became  a 
rusty  red  to  brown.  The  size  of  the  colonies  was  still  small  but  the 
growth  was  very  dense.  In  most  of  the  other  cultures  the  colonies 
covered  the  plates. 

For  a  time  the  growth  still  increased  in  many  cultures  and  the 
colors  grew  more  and  more  brilliant,  then  finally  became  dull  and 
dingy. 

Zonation  was  apparent  in  many  cultures  (PI.  IX.,  Fig.  2),  becom- 
ing very  marked  in  certain  sugar  media  where  it  was  due  to  alternate 
zones  of  profuse  and  sparse  branchings  and  to  hyphal  swellings  filled 
with  coloring  matter. 

Alkalin  cultures  were,  for  the  most  part  colorless,  but  they  event- 
ually became  a  pale  yellow  often  with  slight  traces  of  blue. 

Twelve  days  after  inoculation  numerous  small  leather  colored 
tufts  were  apparent  on  the  surface  of  the  growth  in  the  lactic  acid  cul- 
ture. A  microscopical  examination  revealed  them  as  masses  of  ma- 
croconidia  of  a  fusarium  type.  (PI.  XL,  Fig.  5).  They  were  borne 
on  short,  much  branched  sporophores,  and  were  fairly  constant  in  size, 
measuring  50-62X4.5X6/A.  Already  many  had  swollen  and  some  had 
germinated.  After  a  careful  search  in  all  other  cultures  they  were 
found  in  large  numbers  in  but  one  and  that  the  medium  made  by 
adding  agar  to  Fermi's  solution.  This  colony  had  the  same  color  as 
that  of  the  lactic  acid  culture  and  the  tufts  of  spores  were  borne  in  the 
same  manner. 

Cultures  made  in  Uschinsky's  fluid  variously  neutralized  gave 
different  amounts  of  mycelium  and  numbers  of  spores.  Macroconidia 
are  produced  rather  abundantly  in  this  fluid.  Microconidia  have  not 
been  found. 

GERMINATION  Spores  germinate  readily,  frequently  very  soon  after 
OF  SPORES  having  been  cut  off  from  the  sporophore.  In  Uschin- 

sky's fluid  90  percent  germinated  in  24  hours  and 
some  of  the  germ  tubes  were  considerably  branched.  In  48  hours  new 
spores  had  been  produced  and  a  few  were  beginning  to  germinate.  In 
Raulin's  fluid  germination  was  very  poor,  and  those  that  did  produce 
germ  tubes  soon  died.  In  distilled  water  the  percentage  of  germinated 
was  very  good  but  subsequent  growth  very  poor. 

Fusarium  III. 

APPEARANCE  The  f°rm  °f  r°t  caused  by  this  organism  is  less  com- 
ON  EARS  plete  in  its  clestructiveness  of  the  ear  than  that  of  the 

other  forms  described.  (PI.  III.,  Fig.  1).  Many  of 
the  infected  ears  have  only  a  few  scattered  diseased  grains  and,  while 
such  corn  is  almost  valueless  for  marketing,  it  can  T)e  utilized  for  feed- 
ing purposes.  Under  certain  conditions,  however,  most  of  the  kernels 
may  become  diseased  and  the  cob  more  or  less  infected. 


1909]  EAR  ROTS  OF  CORN  91 

The  mycelium  is  white,  very  sparse,  and  is  found  principally  in 
the  ends  of  the  kernels  where  it  feeds  upon  the  starch  and  produces 
large  numbers  of  spores,  mostly  microconidia.  In  old  dried  specimens 
of  corn  the  hyphae  are  more  or  less  swollen  and  slightly  constricted  at 
the  septa,  and  frequently  contain  many  large  globules.  (PL  XL,  Fig. 
10). 

GROWTH  IN  On  boiled  rice  growth  is  fairly  rapid.     The  mycelium 

CULTURE  is  moderately  dense  and  almost  immediately  begins  to 

produce  spores  and  to  have  a  •  faint  pink  to  salmon 
color.  The  color  never  becomes  very  dense  and  with  age  fades  some- 
what. The  hyphae  are  fairly  constant  in  diameter  in  both  cultures  and 
on  the  corn,  measuring  about  4  to  5/x. 

The  spores  vary  considerably  in  size  and  are  mostly  one  and  two- 
celled,  altho  those  possessing  three  cells  are  not  rare  on  certain 
media.  Microconidia  range  in  size  from  12-15X3. 5-5 p.,  while  the 
macroconidia  are  24-30X35-5.5/A.  (PL  XL,  Fig.  9). 

On  a  plate  of  agar  made  from  an  extract  of  canned  sweet  corn, 
made  -\-lO  with  hydrochloric  acid,  there  was  a  fair  growth  in  2  days 
and  some  spores  of  both  kinds  had  been  produced.  In  one  week  the 
colony  had  become  1.5  inches  in  diameter,  growth  dense,  all  submerged, 
and  a  slight  pink  color  had  developed  at  the  center.  The  protoplasm 
was  very  granular.  The  colony  finally  covered  the  entire  plate.  A 
little  aerial  growth  developed  at  the  center  and  a  pink  to  red  color 
was  distributed  thruout  the  plate. 

In  the  same  medium,  made  — 10  with  sodium  hydroxid,  growth 
was  good  from  the  beginning,  becoming  1.5  inches  in  diameter  in  4 
days.  Both  kind  of  spores  were  abundant.  The  color  remained 
white.  Some  of  the  hyphae  were  5.5  to  6/x  in  diameter. 

In  the  check  plate,  containing  sweet  corn  extract  agar  alone,  a 
rather  rapid  development  took  place  and  both  types  of  spores  were 
present  in  2  days.  The  colony  finally  covered  the  plate  and  changed 
from  a  pale  pink  to  a  pale  blue  color. 

Growth  in  cocoanut  milk  agar  was  very  rapid  and  possessed  more 
aerial  mycelium  than  any  of  the  above.  The  color  was  white  dotted 
with  pink  tufts  of  spores.  Some  hyphal  swellings  developed  and  both 
kinds  of  spores  were  present.  The  growth  became  pale  blue,  and 
eventually  deep  purple  in  color. 

In  a  few  cultures  on  boiled  rice  there  developed  some  small  rather 
firm  bodies  of  a  pink  and  finally  a  rusty  color,  which  resembled  scle- 
rotia.  Some  of  these  were  sectioned  in  paraffin  and  were  found  to  be 
made  up  of  a  mass  of  hyphae  grown  closely  together.  They  were 
watched  for.  some  time  but  never  came  to  maturity. 

BACTERIA 

The  corn  plant  in  the  field  is  subject  to  attack  by  several  kinds  of 
bacteria,  producing  various  forms  of  disease.  The  developing  ears  do 
not  escape  injury  from  this  source,  but  the  loss  sp  caused  seems  to  be 
small  compared  with  that  from  the  fungi  heretofore  described — almost 


92  BULLETIN  No.  133  [February, 

negligible  from  a  practical  standpoint.  Whether  these  ear-infections 
are  all  due  to  the  same  species  of  bacteria  has  not  been  ascertained. 

Certain  ears  when  stripped  of  the  husks  show  grains  which  are 
evidently  diseased,  rather  uniformly  distributed  among  the  sound  ker- 
nels or  in  small  groups  on  some  part  of  the  ear.  The  diseased  kernels 
are  dark  in  color,  often  corroded  upon  the  surface,  and  are  brittle  in 
texture.  Sometimes  a  shiny,  mucilaginous  or  gum-like  exudate  is 
noticeable  upon  the  outer  surface  of  the  grains.  Upon  microscopical 
examination  this  exudate  is  found  to  be  made  up  of  a  pure  culture  of 
a  medium  sized  bacillus  of  short,  cylindrical  shape  and  capable  of  rapid 
ciliate  movement.  These  are  present  in  myriads  and  what  appears  to 
be  the  same  organism  is  found  in  great  numbers  in  the  crumbling, 
starchy  portions  of  the  affected  grains.  A  conspicuous  characteristic 
of  such  diseased  kernels  is  the  red  color  taken  on  by  the  substance  of 
the  scutellum.  When  such  grains  are  divided  lengthwise  thru  the 
flat  surfaces  the  starchy  portion  is  seen  to  be  distinctly  white,  while 
that  known  as  the  chit  is  as  distinctly  red. 

The  infection  seems  to  begin  externally  with  the  silk  and  the  bac- 
teria follow  a  strand  of  this  to  its  attached  kernel,  explaining  how  it 
comes  about  that  any  one  of  the  latter  upon  the  cob  may  be  diseased 
among  those  adjoining  healthy.  Where  these  bacteria  otherwise  live 
has  not  been  ascertained. 

The  bacteria  of  the  growing  corn  plant  is  a  subject  well  worth 
special  study. 

PREVENTION 

The  diseases  of  corn  (maize)  described  in  this  Bulletin  should  not 
be  confounded  with  corn  smut  which  is  frequently  seen  upon  the  ears 
as  well  as  on  other  parts  of  the  corn  plant.  This  is  easily  recognized 
and  is  well  known  on  account  of  the  large  outgrowths  of  a  black  or 
sooty  substance  which  when  dry  readily  falls  into  fine  dust.  The  ear 
rots  under  discussion  are  very  different  and  are  best  characterized  as 
moldy  in  appearance.  There  is  a  white -or  pinkish,  cobwebby,  closely 
adherent  growth  on  and  in  the  husks,  silk,  grain,  and  cob  or  any  of 
them.  The  affected  ears  are  never  perceptibly  dusty,  but  later  become 
brittle  or  friable  and  merit  the  name  sometimes  applied — dry  rot. 

The  life  history  of  the  fungus  (Diplodia  Zeae)  causing  most  of 
these  ear  rots  (about  90  percent)  has  now  been  sufficiently  worked 
out,  as  detailed  above,  to  make  it  possible  to  recommend  preventive 
measures  with  confidence  in  the  prescriptions.  This  fungus  lives  as  a 
parasite  on  the  ears  of  the  corn  plant  and  apparently  on  no  other  por- 
tion of  the  plant.  At  first  it  was  natural  to  suppose  that  a  seasonal 
infection  must  be  due  to  the  wintering  over  on  the  old  diseased  ears, 
and  that  in  all  probability  a  careful  collection  of  these  at  the  time  of 
husking  would  do  much  towards  the  reduction  of  the  malady  in  the 
field  the  following  year.  This  may  be  true  to  a  considerable  extent, 
but  the  discovery  that  the  same  fungus  develops  abundantly  upon  the 
dead  stalks,  even  upon  those  that  have  lain  on  the  ground  two  years 
and  are  therefore  much  decayed,  changed  materially  conclusions  upon 


1909]  EAR  ROTS  OF  CORN  93 

the  subject.  It  will  not  be  surprising  if  it  is  hereafter  found  that  the 
fungus  does  sometimes  live  on  other  parts  than  ears  of  growing  corn, 
neither  is  it  impossible  that  it  develops  as  a  saprophyte  on  something 
besides  corn  stalks.  It  can  be  rather  confidently  asserted,  however, 
that  these  things  if  true  at  all  must  be  rare  occurrences  in  Illinois  corn 
fields,  and  that  for  practical  purposes  attention  may  be  centered  en- 
tirely upon  the  facts  now  made  known. 

Little  dependence  can  be  placed  upon  any  direct  treatment  of  the 
soil,  any  outward  application  to  the  plant,  any  variation  in  time  of 
planting,  any  selection  of  varieties,  or  other  similar  matters,  tho 
there  may  be  some  difference  at  different  times  and  under  special  con- 
ditions on  account  of  any  such  variations  connected  with  the  soil  or 
with  the  plant.  A  few  cases,  indeed,  have  been  observed  where  the 
amount  of  rot  was  undoubtedly  traceable  to  some  such  difference,  now 
one  thing,  now  another.  But  there  is  not  enough  of  this  to  alter  the 
recommendations  that  can  now  be  made. 

It  is  best  then  to  give  attention  principally  if  not  solely  to  the 
active  agent  which  causes  the  destruction.  Rot  does  not  occur,  as  has 
been  shown,  under  any  circumstances  or  condition  except  as  it  is  di- 
rectly brought  about  by  the  fungus,  and  the  fungus  cannot  start  ex- 
cept by  its  own  reproductive  methods.  Keep  the  spores  away  from 
the  green  ears  and  the  corn  will  remain  sound.  Keep  the  fields  free 
from  the  substance  on  which  spores  are  produced  from  the  beginning 
of  a  season  for  infection,  and  the  crop  must  remain  free  from  danger 
in  this  regard. 

Undoubtedly  there  is  some  dissemination  of  spores  from  the 
earlier  affected  ears  to  sound  ones  of  the  same  season,  but  here  again 
the  probable  amount  of  loss  so  caused  is  small.  Practically  the  new 
infection  comes  from  the  old  stalks — those  one  and  two  years  old — 
and  therefore  these  must  have  chief  attention  in  the  combat.  From 
this  it  is  easy  to  see  what  procedure  should  be  adopted  in  trying  to  re- 
duce the  rot  in,  or  eliminate  it  from,  the  field.  Stated  in  a  word,  it  is 
carefully  to  take  out  of  the  field  and  destroy  the  rot-infected  ears  at 
the  time  of  husking,  with  the  view  of  reducing  the  amount  of  the 
fungus  later  on  the  stalks;  then  to  remove  from  badly  infected  fields 
the  stalks  by  low  cutting  and  hauling  away  or  by  burning,  or  better 
still  by  such  rotation  of  crops  that  corn  shall  not  follow  corn  within  a 
period  of  two  years.  Care  should  also  be  taken  not  to  plant  corn  by 
the  side  of  an  old  infected  field  especially  if  the  latter  is  upon  the  side 
from  which  come  the  prevailing  summer  winds — the  south  and  west. 

As  corn  is  commonly  cut  for  fodder  or  for  silage,  there  may  be 
stumps  enough  left  to  carry  over  too  much  of  the  disease,  and  old 
stalks  may  get  back  again  with  the  manure  to  a  detrimental  extent ; 
tho  by  attention  to  these  matters  there  must  be  a  possibility  of 
causing  a  decided  diminution  of  the  trouble  by  such  early  removal  of 
the  stalks. 

Unless  the  old  stalks  zvith  their  harboring  fungus  are  effectually 
destroyed,  corn  should  not  be  planted  again  zvhere  there  has  been  much 


94  BULLETIN  No.  133  [February, 

of  the  disease  for  two  years  thereafter,  nor  nearer  than  20  to  30  rods, 
especially  on  the  windward  side,  of  an  old  corn  field  badly  infected  one 
or  two  years  before. 

HISTORY  AND  SYNONOMY  (DIPLODIA  ONLY) 

Schweinitz  in  his  Synopsis  Fungorum  Carolinae  (1822),  number 
79y  described  a  fungus  found  on  old  stalks  of  maize  which  he  called 
Sphaeria  Zeae.  Later  in  his  Synopsis  Fungorum  in  America  Boreali, 
[North  American  Fungi]  page  207,  number  1451,  he  again  described 
the  same  fungus  on  the  same  plant  under  the  same  name  as  follows : 

"Omnino  tecta,  epidermide  fusco  tincta  (ostiolis  solis  prominulis)  satis 
elevata.  Seriatim  disposita,  brevis,  utrinque  acuminata,  subconfluens.  Peri- 
thecii  binis  vel  ternis  tantum  in  caespitulo,  subdistantibus,  primum  albofarctis, 
demum  evacuatis.  Ostiolis  latis,  umbilicatis,  saepe  unico." 

This  may  be  translated  as  follows : 

Entirely  covered,  epidermis  fuscous  colored,  rather  elevated  (ostiola  alone  a 
little  prominent).  Distributed  in  series,  short,  acuminate  at  both  ends,  subcon- 
fluent.  Perithecia  only  two  or  three  in  a  group,  subdistant,  at  first  white  within, 
at  length  evacuated.  Ostiola  broad,  umbilicate,  often  to  a  marked  degree. 

In  the  latter  work,  under  number  1866,  the  author  refers  to  num- 
ber 234  of  Synopsis  Fungorum  Carolinae,  and  classifies  what  seems  to 
be  the  same  fungus  as  Dothidea  Zeae,  but  there  is  no  mention  in  either 
case  of  asci.  This  was  before  the  day  of  the  compound  microscope  as 
a  serviceable  instrument,  which  sufficiently  accounts  for  the  absence 
of  finer  details  in  the  descriptions. 

In  1847  Berkeley,  in  Hooker's  London  Journal  of  Botany  6:326 
described  a  fungus  from  the  stalks  of  maize  which  he  called  Sphaeria 
Maydis,  and  appended  the  following  description  quoted  in  Ellis  and 
Everhart,  North  American  Pyrenomycetes  page  452 : 

"Spots  minute,  elevated,  often  purple-brown,  punctiform  or  subelliptical, 
rarely  linear,  containing  very  few  perithecia,  with  a  single,  broad-conical  ostio- 
lum.  Sporidia  oblong,  slightly  curved,  uniseptate.  Habit  that  of  Leptospaeria 
arundinacea*  Very  different  from  Sphaeria  (Diplodia)  Zeae,  Schw." 

These  descriptions  seem  to  characterize  different  species  and  ap- 
parently justify  the  remark  by  Berkeley  that  the  fungus  at  the  time  in 
his  hands  was  very  different  from  that  earlier  described  by  Schweinitz. 

But,  probably  more  from  this  remark  than  from  anything  else, 
most  subsequent  writers  have  referred  the"  fungus  observed  by  many 
on  old  stalks  of  corn  and  identified  as  a  Diplodia  to  Berkeley's  species. 
Thus  Saccardo,  in  Sylloge  Fungorum,  3:373,  (1884),  writes  Diplodia 
Maydis  (Berk.)  Sacc.,  and  quotes  Sphaeria  Maydis  Berk.,  Lond.  Jour, 
of  Bot.  6:326,  as  a  synonym,  together  with  in  the  same  way,  Diplodia 
Zeae  Lev.,  Ann.  Sc.  Nat.  III.  9 : 258,  and  Sphaeria  Zeae  Curr.,  Simple 
Sphaer.  n.  358,  f.  128.  So  far  as  these  references  are  concerned,  Sac- 
cardo properly  takes  Berkeley's  name,  for  this  was  published  in  1847 
while  the  dates  for  the  others  are  respectively  1848  and  1859.  Leveille 
however  founded  his  name  upon  Sphaeria  Zeae  Schw.,  which,  as 
shown  above,  dates  back  to  1822.  If,  therefore,  the  plant  so  called 
is  the  same  as  that  named  by  Berkeley  Sphaeria  Maydis,  the  latter 
name  becomes  a  synonym.  Notwithstanding  the  statement  by  Berke- 


1909]  EAR  ROTS  OF  CORN  95 

ley  that  the  two  plants  are  very  different,  there  is  now  much  reason  to 
suppose  they  are  really  the  same,  or  at  least  that  specific  distinction 
cannot  be  maintained.  The  reference  by  Saccardo  to  Currey  is  based 
upon  a  paper  by  the  latter  in  the  Trans.  Linn.  Soc.  22:330  (Simple 
Sphaer.)  appearing  in  1859  upon  the  fungi  in  the  Hooker  Herbarium — 
this  particular  material  undoubtedly  coming  from  America  and  prob- 
ably collected  by  Schweinitz.  Though  finding  no  asci,  Currey  retains 
the  genus  relation  and  identifies  the  specimens  as  Sphaeria  Zeae  Schw. 
The  spores  as  figured  (PI.  59,  f.  128)  agree  very  well  with  those  of  our 
plant.  Moreover  reference  is  made  to  Fries,  Sys.  Fung.  2  :527  where 
S.  Zeae  Schw.  is  referred  to  (1823).  This  can,  therefore,  be  none 
other  than  the  Schweinitzian  plant,  and  if,  as  Saccardo  thinks,  the 
name  is  a  synonym  of  S.  Maydis  Berk,  the  two  names  must  apply  to 
the  same  species. 

The   exsiccati    specimens   examined   show   no   differences   which 
should  indicate  specific  distinctness.     These  are: 
Diplodia  Zeae  Schw. 

Ravenel,  Fung.  Car.  n.  74  (1852) 
Diplodia  Zeae  Lev. 
Sphaeria  Zeae  Schw. 

Thiimen,  Myc.  Univ.  n.  1194  (1878) 
Diplodia  Zeae  Lev. 

Ellis,  N.  A.  Fungi  n.  31  (1878) 
Diplodia  Zeae  ( Schw. ) 

Ravenel,  Fung.  Amer.  n.  393  (1879) 
Diplodia  Maydis  (Berk.)  Sacc. 

Roumeguere,  Fung.  Gall.  n.  5378  (1890) 
Diplodia  Zeae  Lev. 

Ellis  and  Everhart  Fung.  Col.  n.  73  (1893) 
Ellis  and  Everhart,  N.  A.  Pyr.  745  say: 

"The  spec,  in  Herb.  Schw.  is  the  same  as  Diplodia  Zeae  Lev.  in  Ell.  N.  A. 
F.  n.  31". 

Assuming  that  Sphaeria  Maydis  Berk,  is  the  same  as  Sphaeria 
Zeae  Schw.,  or  that  the  former  name  really  applies  to  some  other 
plant  than  that  with  which  we  are  dealing,  there  can  be  no  reasonable 
doubt  that  the  fungus  described  in  this  Bulletin  should  be  called  Diplo- 
dia Zeae  (Schw.)  Lev.,  until  this  form  is  proved  to  be  genetically  con- 
nected with  something  of  higher  fruiting.  Many  surmises  of  the  lat- 
ter kind  have  been  made ;  Schweinitz  himself  made  it  a  species  of 
Sphaeria  and  was  followed  in  this  by  Berkeley  and  Currey  as  noted 
above.  The  former  also  identified  another  specimen  as  a  Dothidea 
(Syn.  Fung.  Bor.  n.  230  (1866)  which  he  subsequently  (Am.  Sc.  Nat. 
III.  9:258)  admitted  to  be  the  same  as  the  one  called  Sphaeria.  Later 
the  name,  Sphaeria  Maydis  Berk,  has  several  times  been  applied  to 
American  specimens  certainly  identical  with  our  plant.  Bennett,  Cat. 
PI.  R.  I.  87,  (1888),  places  it  in  Dothiora,  and  Ellis  and  Everhart,  N. 
A.  Pyr.  452,  (1892),  assigns  it  to  Diaporthe.  But  there  is  no  evidence 
that  these  writers  had  before  them  perithecia  with  asci  or  that  they  had 


96  BULLETIN  No.  133  [February, 

anything  more  than  is  usually  to  be  found  in  the  examination  of  or- 
dinary specimens.  There  is  no  proof  known  to  the  present  writers 
that  a  mature  or  ascus  stage  exists,  though  there  are  such  forms  not 
infrequently  associated  with  the  Diplodia  on  old  culms  of  maize.  Our 
cultures  of  the  latter  though  both  varied  and  prolonged  have  not  dem- 
onstrated further  fruiting.  Diaporthe  incongma  E.  &  E.,  and  D.  Kel- 
lermanniana  Winter,  are  both  (if  they  are  distinct)  found  on  decaying 
culms  of  Zea  Mays,  N.  A.  Pyr.  453. 

The  first  suggestion  in  print  that  this  fungus  works  as  a  parasite 
seems  to  be  the  Heald,  Science,  N.  S.  23  :624  (1906),  where  the  follow- 
ing note,  under  the  title,  "New  and  Little-known  Plant  Diseases  in 
Nebraska,"  is  given : 

"Moldy  corn   due  to  a  fungus  provisionally  referred  to  Diplodia  Maydis, 
but  differing  in  several  points  in  habit  and  structure." 

One  of  us,  Barrett,  Science  N.  S.  27:212-213  (1908),  describes 
under  "Dry  Rot  of  Corn  and  Its  Causes"  something  of  the  effects  of 
Diplodia,  "very  probably  Diplodia  Maydis",  as  a  parasite  upon  corn 
and  briefly  relates  its  life  history.  Further  citation  upon  the  same  is, 
Burrill  and  Barrett,  Circ.  111.  Ag.  Sta.  n.  117:1-3,  (1908).  Here,  too, 
mention  is  made  of  similar  rots  due  to  species  of  Fusarium  and  by 
bacteria. 

Heald,  Wilcox  and  Pool,  Reprint  from  the  Twenty-second  Annual 
Report  of  the  Nebraska  Agricultural  Experiment  Station,  distributed 
January  1,  1909,  give  a  good  description  of  the  fungus,  called  by  them 
Diplodia  Zeae  (Schw.)  Lev.,  and  of  its  work  as  a  parasite  upon  corn. 
Excellent  plates  accompany  the  text. 

The  fungus  must  for  the  present  be  cited  under  the  genus  Diplo- 
dia and  the  synonomy  seems  to  be  as  follows : 

Diplodia  Zeae  (Schw.)  Lev. 
Sphaeria  Zeae  Schw.     1828 
Dothidea  Zeae  Schw.     1831 
Sphaeria  Maydis  Berk.     1847 
Diplodia  Zeae   (Schw.)   Lev.  1848 
Diplcfdia  Maydis  (Berk.)  Sacc.     1884 
Dothiora  Zeae  (Schw  )  *Bennett  1888 
Diaporthe  Maydis  (Berk.)     Ell.  and  Ev.     1892 

Thru  the  courtesy  of  Dr.  Farlow,  Mr.  A.  B.  Seymour  exam- 
ined, in  the  collections  of  the  former,  certain  of  the  specimens  enum- 
erated above ;  and  gave  from  the  notes,  prepared  for  publication  other- 
wise, citations  to  literature  embracing  all  the  above  names.  From 
these  notes,  Mr.  Seymour  arranged  the  synonomy  as  it  is  above.  This 
latter  was  communicated  in  a  letter  dated  July  30,  1908. 

It  should  be  said  that  the  manuscript  for  this  Bulletin  was  prac- 
tically completed  during  August,  1908,  but  was  not  sent  to  the  printer 
untif  February  8,  1909. 

*  Bennett   wrote:    Dothiorq  Zeae   Lcr, 


19*09]  EAR  ROTS  OF  CORN  97 

DESCRIPTION  OF  PLATES 

Plate  I.  Fig.  1. — An  ear  of  sweet  corn  thirteen  days  after  inocu- 
lating in  the  tip  with  spores  of  Diplodia  Zeae.  Fig.  2. — Another  ear 
of  the  same,  inoculation  at  base. 

Plate  II.  Fig.  1. — An  ear  of  corn  infected  with  Fusarium  I. 
Fig.  2. — An  ear  of  corn  showing  the  effect  of  Fusarium  II. 

Plate  III.  Fig.  1. — Field  corn  with  scattered  individual  kernels 
infected  with  Fusarium  III.  Fig.  2. — A  longitudinal  section  of  an  ear 
of  corn  showing  the  small,  black  pycnidia  in  the  cob  toward  the  outside. 

Plate  IV.  Fig.  1. — An  ear  of  sweet  corn  destroyed  by  Diplodia 
Zeae,  spores  of  which  were  inserted  into  the  shank  bearing  the  ear. 
Fig.  2. — Ear  of  sweet  corn  artificially,  inoculated  and  photographed 
after  being  in  the  laboratory  seven  days.  The  black  color  about  the 
base  of  the  ear  is  due  to  numerous  pycnidia. 

Plate  V. — Two  shanks  of  the  corn  plant  bearing  numerous  pycni- 
dia of  Diplodia  Zeae  as  small  black  specks.  These  shanks  were  collect- 
ed in  the  spring. 

Plate  VI.  Fig.  1. — A  piece  of  old  corn  stalk  showing  pycnidia 
of  Diplodia  Zeae.  Fig.  2. — Piece  from  the  same  stalk  as  Fig.  1  after 
soaking  in  water  fifteen  hours  and  keeping  moist  for  a  few  days  in 
a  damp  chamber.  The  black  masses  are  tendrils  of  Diplodia  spores. 
Fig.  3. — A  single  pycnidium  of  Diplodia  Zeae  on  a  corn  stalk  show- 
ing the  exuded  tendril  of  spores  and  the  internal  cavity. 

Plate  VII.  Fig.  1. — A  cross  section  of  an  ear  of  corn  showing 
Diplodia  pycnidia  as  black  specks  in  the  cob.  Fig.  2. — A  photograph 
of  germinating  spores  of  Diplodia  Zeae. 

Plate  VIII.  Fig.  1. — A  photomicrograph  of  Diplodia  spores  from 
an  ear  of  diseased  corn.  Fig.  2.- — Diplodia  spores  from  a  rice  tube 
culture. 

Plate  IX.  Fig.  1. — A  petri  dish  containing  corn  meal  extract  agar 
and  5  percent  galactose  in  which  are  imbedded  numerous  pycnidia 
of  Diplodia  Zeae.  Fig.  2.— A  sweet  corn  agar  plate  showing  zonation 
of  Fusarium  II. 

Plate  X.  Fig.  1. — A  cross  section  of  a  pycnidium  of  Diplodia  Zeae 
on  a  corn  stalk.  Fig.  2. — A  cross  section  of  a  pycnidium  of  Diplodia 
Zeae  on  a  kernel  of  corn. 

Plate  XL  Fig.  1. — Spores  of  Diplodia  from  corn.  Fig.  2. — 
Young  spores  with  sporophores  attached.  Fig.  3. — Germinating  Dip- 
lodia spores.  Fig.  4. — Short,  more  or  less  swollen,  and  darkened 
branches  of  Diplodia  hyphae.  This  indicate  the  beginning  of  pyc- 
nidia formation.  Fig.  5. — Macrdconidia  of  Fusarium  II.,  some  of 
which  are  beginning  to  germinate.  Fig.  6. — Mycelium  of  the  same 
fungus.  Fig.  7. — Starch  grains  from  a  corn  kernel  infected  with 
Fusarium  II.,  showing  the  corrosive  effect.  Fig.  8. — Sporophores  of 


All  drawings  and  photographs  were  made  by  James  T.  Barrett  except  Plate  I.,  which 
was  executed  in  colors  by  Mrs.  Flora  M.  S4ms.  (The  reproduction  as  Plate  1  is  not  in 
color,  but  a  colored  duplicate  accompanies  a  part  of  the  issue). 


98  BULLETIN  No.  133  [February, 

Fusarium  II.,  drawn  at  1 1 :30  a.  m.  and  at  1 :30  p.  m.  to  show  the 
rate  of  development  of  the  spores  in  culture.  Fig.  9. — Microconidia 
and  macroconidia  of  Fusarium  III.  from  culture.  Fig.  10. — Mycelium 
of  the  same  from  a  corn  kernel.  Fig.  11. — Microconidia  and  macro- 
conidia of  Fusarium  I.  from  a  prune  agar  plate.  Fig.  12. — Same  from 
an  infected  ear  of  corn.  Fig.  13. — A  spore-producing  hypha  from  a 
young  prune  juice  culture.  Fig.  14. — Germinating  spores  of  Fusarium 
I.  Fig.  15. — Spores  of  Fusarium  I.  from  a  dried,  diseased  embryo 
ear  of  corn.  Fig.  16. — A  hyphal  branch  of  Fusarium  I.  producing 
both  microconidia  and  macroconidia. 


1909] 


EAR  ROTS  OF  CORN 


99 
PLATE  I. 


FIGURE  1.     INOCULATED  IN  THE  SILK        FIGURE  2.    INOCULATED  AT  THE  BASE 
WITH  DIPLODIA.  WITH  DIPLODIA. 


100 


BULLETIN  No.  133 


[February, 
PLATE  II. 


FIGURE  1.     FUSARIUM  I. 


FIGURE  2.     FUSARIUM  II. 


1909] 


EAR  ROTS  OF  CORN 


101 
PLATE  TIT. 


FIGURE  1.     FUSARIUM  III. 


FIGURE  2.     DIPLODIA. 


BULLETIN  No.  133 


[February, 
PLATE  IV. 


FlGURii    1.      DlPLODIA. 


FIGURE  2.    DIPLODIA. 


1909] 


EAR  ROTS  OF  CORN 


103 
PLATE  V. 


DIPLODIA  ON  OLD  SHANKS. 


104 


BULLETIN  No.  133 


[February, 
PLATE  VI. 


DIPLODIA  ON  OLD  STALKS.    FIGURE  1,  DRY.    FIGURE  2,  AFTER  KEEPING  MOIST. 
FIGURE  3,  EXUDING  SPORES  (MAGNIFIED). 


1909] 


EAR  ROTS  OF  CORN 


105 
PLATE  VII. 


DIPLODIA.    FIGURE  1,  PYCNIDIA  ON  COB.    FIGURE  2,  GERMINATING  SPORES. 


106 


BULLETIN  No.  133 


[February, 
PLATE  VIII. 


DIPLODIA  SPORES.    FIGURE  1,  FROM  DISEASED  EAR.    FIGURE  2,  FROM  A  CULTURE. 


1909] 


EAR  ROTS  OF  CORN 


FIGURE  1,  DIPLODIA  CULTURE  SHOWING  PYCNIDIA.    FIGURE  2,  FUSARIUM  II. . 
CULTURE  SHOWING  ZONATION. 


108 


BULLETIN  No.  133 


[February, 


PLATE  X. 


PYCNIDIA  OF  DIPLODIA  :  FIGURE  1,  FROM  STALK.    FIGURE  2,  FROM  CORN  KERNEL. 


1909] 


EAR  ROTS  OF  CORN 


JTJ3.  de(. 
SPORES,  ETC.:   FIGURES  1  TO  4,  DIPLODIA;  THE  OTHERS  FUSARIUM. 


